Teleport to the Tomb of Oedon lamp and go backwards towards the bridge where a Brick Troll drops a flaming boulder on enemies. Don't attack anything, let the troll kill the enemies and grant you 100+ echoes. Repeat.
Assuming you have defeated the Darkbeast Paarl -- Spawn at the Graveyard Of The Darkbeast Lamp. Walk directly forward through the giant door. You will encounter 4 Scourge beasts and 3 Beast patients. Playing NG+ with all 3 Moon runes you get roughly 70k echoes each run and it takes less than 2 minutes each time. All the beasts end up as 1 on 1 fights if you move quickly and are very easy. The Scourge Beasts also drop blood stone shards and multiple blood vials.
There is also another early game route, however it's for a bit lower levels. It only requires you to have killed the Cleric beast. It does however usually drop a lot of vials and quicksilver bullets. You can find it here.
Warp to the Witches' Abode lamp and head straight back toward the first Hemwick Charnel Lane lamp killing everything along the way. The three axe guys yield about 2500 echoes apiece, and at night there are two smoke demons worth 1500 ( the second smoke demon spawns just outside the entrance to the Hemwick area). One run nets about 15k echoes with the first tier Moon rune equipped.
One run should take you about two and a half minutes, and you can buy Hunter's Marks around mid game for 1800 each. Since each run nets around 16-18k, one run should yield enough echoes to buy tons of Marks and save time at the the end of the run by using a mark instead of going back through Dream. Around 250k/hr (NeoMerdien - video showing the above method (22k echoes for 2:30 minutes using Heir and Moon rune).)
The Orphanage offers a good place to farm blood echos after you have opened the last shortcut.(Orbonis - video showing the run through the Orphanage)
Killing all the spectral ladies and servants in the entrance hall to Cainhurst Castle also yields about 16k echoes if both the first and second floors are cleared.
Starting from the Mergo's Loft: Base lamp, kill the three giants right down the path by either DPSing them or easily knocking them off the ledge with a heavy weapon for a yield of about 11-15k blood-echoes (depending on rune set up) per clear. Done right, all three giants should take under 30 seconds to kill, and jumping off the ledge next to the two giants will spawn you back at the lamp with your echoes on the third giant. Rinse and repeat for easy farming before Mergo's Loft: Middle. Beware that the giants can potentially one shot you if you lack vitality, so proceed with caution when retrieving echoes.
A good late game farming spot for echos and blood vial is the Mergo's Loft: Middle lantern. Glyph all the Moon Glyphs you have and head upstairs to the 2 katana guys. Each one gives around 3k echos with a chance of 2-4 blood vials. It's easy to kill them one by one (just use pebbles to pull them). Head upstairs to kill the third guy. Further down the road is a giant pig (nightmare edition) looking away from you. I found it very easy to backstab these pigs. each pig gives you around 11-12k echos. There are 2 more pigs down the road. Try to pull them separately and you will have an easy time to kill them. Without a lot of testing i made around 50k echos in 3 minutes + the chance of blood vials. Return with the Bold Hunter's Mark to reset the enemies and start over again. Additionally, you can run past the pigs (be careful) and aggro the group of 4 Shadows of Yharnam. After doing so, there's a staircase to your left, head down it. The Shadows and Pigs will focus on each other instead of you and a battle royale ensues - where you get to keep the echoes. The Shadows will kill the pigs most times, leaving one wounded shadow behind for an easy kill. This nets you the 10-11k echoes each from the pigs and an additional ~3k souls from each shadow.
Alternative approach: equip 3 Heir runes (or best Moon and 2 Heir runes). From "Mergo's Loft: Middle" run straight to the first pig, ignore shadows. You don't have to be sneaky, just run and visceral attack it. Now run to the next 2 pigs. Using Saw Cleaver and charged attack it's possible to quickly visceral the pig in the back. Run between two pigs, position yourself beside the second one and facing the road ahead perform charged attack. The curvature of the attack allows to stun the pig without standing directly behind it. Dealing with one pig that is left is easy. Use Bold Hunter's Mark to respawn enemies and repeat. With 1 Moon and 2 Heirs available from normal game, you can get around 67k echoes each time. That's 200k echoes for the price of 3 Bold Hunter's Marks. Around 1mln echoes per hour (on NG).
Another good location is the first floor lecture room. The large group of enemies in the right lecture room are extremely weak to fire (2 hits with an un-upgraded hunter's torch killed them) and the total group all together will give roughly just over 10k echoes. With the current system of respawning enemies, you may head over to the lecture room across from your current one, and let the single enemy kill you; you will be brought back to the nearby lantern, forgoing the need to teleport to the hunter's dream and back.
There is also a second system, where you run down to the first floor, and can run between the two lamps. This way, you also get to meet Patches the spider if not met. You will also get to kill the giant, and get twin bloodstone shards. There is a brilliant video Here that shows you how to net about 52559 echoes in about 3,5 minutes, and loads of quicksilver bullets. The video shows it in a good way, so i recommend you watch it.
One of the best locations is the Mergo's Loft: Base. If you have Ludwig's Sword leveled up to at least level 8, equip your moon runes, sneak up on the first fur giant, use the hold R2 attack so he falls to his knees, and then visceral him. Afterwards, kill the next two fur giants. Within 2 minutes, you'll clear 18k blood echos. Bring plenty of bold hunter marks to repeat quickly in succession.
You can also do a route at the Witches' Abode for late game, not too dissimilar from the one in the Early/Mid game section, except that this one is based around runes gained somewhat late in the game. The 3 runes you would want to use are Moon Tier 2 and 3 (20% & 30% more echoes dropped) and the strongest Heir rune (40% more echoes from V.ATK). You start off by running up the stairs and killing the 3 enemies there, run down the hill and use a visceral attack on the big axe guy running up towards you. After him you run down and use visceral attack to kill both of the axe guys walking around, then you run left towards the destroyed bridge, killing all the dogs and the molotov tossing lady. This takes about 1 minute and 30 seconds, granting you ~27,000 echoes. If you desire to run the route several times it's recommended to jump of the bridge into the water to respawn at the Witches' Abode lamp. (Just remember to pick up your echoes again before jumping off another time!)
Pretty good strategy for farming echos, netting about 200k/2:30min (Using all 3 Moon) Load up the Lower Loran Chalice, run to the next lantern, turn left, across the bridge, up the stairs, kill the spider past the door, across the next bridge, kill the silver beast guarding the lever, drop off the bridge onto the other to put you back at the main room, and run to the boss. The boss is another Silver Beast and once he's down hit the lantern back to the Dream, rinse and repeat.
Farm Isz Chalice with all 3 Moon Runes. First 2 bosses are a piece of cake and each run will net you around 400,000 plus. Search for Isz Chalice, join chalice, kill first 2 bosses, remove chalice, repeat. Once you get a good feel for these bosses (Brainsucker and Celestial Emissary), you should be able to finish in about 10 minutes.
First and foremost, let me add for you my (as I refer to it, high mid range) echo farming guide (video follows) which I am adding in the case that you desire a viable echo garnering setting but with the added bonus of a high propensity of Blood Stone Chunks dropping for you (werewolves):
For my "high range" echo guide you will simply not find a more lucrative (in terms of echo garnering) chalice run than my current (it is public for your usage) discovered scenario. If ran, from start to end, with the three versions of the Moon Rune(s), a player will net a total of 3.1 million echo's.
Note: Chalice code - qifg37ku
Note #2: The cache from this chalice include - Lake (7%), Clockwise Metamorphosis (15%), & Lost Reiterpallasch
Edit: this chalice does give about 3 million echoes for a full run, but it's a very difficult chalice and doesn't have a particular spot good for farming. The bosses are the undead giant, watchdog, and bloodletting beast. Considering the time it takes to get through the dungeon, most if not all people would be better off with one of the lower-echo methods that is easier and faster. I did find both runes, though, but no sign of the weapon.
- A set of three Heir Runes, vs. the set of three Moon Runes yield far more echoes, when doing visceral attacks.
- The area just before the Wetnurse's Lunariam has three boars, and 9 other targets which all are susceptible to riposte attacks, and yield incredible echoes, and vials.
- It's best to use a weapon that doesn't kill the boars after using one visceral attack, stacking visceral attacks yields even more blood echoes.
- Being co-operator and farm the First Hunter by continously knocking down him with Burial Blade charge attack, 64000 echo for each kill.
- Up to 100k Echoes per minute. You've to gain access to the Great Isz Chalice dungeon, the layout is fixed. In Layer 3 after the lamp is a big room filled with these blue alienlike creatures. They can be slaughtered easily. Kill the first group, run past the werewolfs, hug to the right wall so they don't follow you. Kill the rest and use a bold hunter's mark. Rinse and Repeat.
- Alternatively, go to Ailing Loren Chalice dungeon, in Layer 2, before the boss room, there's a room contained with Beast Patients, Wolf Beasts and Red Spiders which spawn infinitely, DO NOT open the gate, instead, sweep them with Burial Blade charge attack since it has wall-piercing property, each spider kill grants 1000 echo with all three Moon runes equipped, however, since they spawn infinitely and spawn pretty quick, one can earn 200k Echos without the use of Blood Hunter Mark, only sweeping the spiders behind the gate effortlessly.
- Also in the Ailing loran chalice: it's possible to earn roughly 58200 echoes in about a minute there is a video describing it Here.
- This run grants 100356 Echoes (with tiers 1, 2 and 3 of the moon rune equiped) per minute. Starting at layer three of the Pthumeru Ihyll chalice, head into the first room and down the ladder. Kill the two Pthumerian miners and go to the end of the tunnel. Aggro the scorpion into the tunnel and kill it (make sure to avoid aggroing the hunter as well). Walk straight out of the tunnel until you're lined up with the hunter's back, then walk up and perform a visceral attack, while he is attempting to recover stun lock him to death (the hunter has a chance of dropping a blood gem). There is also a Wandering Madness right beside the hunter which drops blood gems.