The Abandoned Lair is located to the south of the Leaf Village, on the Ledge Forest Encampment map which is east of the Ledge Forest. The Lair has multiple rooms and levels, as well as traps laid for ninja curious enough to explore it. In Addition, the Lair is infested with Snakes and Venomous Snakes, both of which drop valuable venom.
Abandoned Lair Entrance
Entering the Abandoned Lair will bring you to the Abandoned Lair Entrance Map. The room is full of Snakes, which sometimes spawn directly at the map transition, so entering using Cloak or Substitution is recommended. This map is perfect for Genin looking to level quickly, because the Snakes can be grouped easily by running around the map in a circle. At the back of the map is a opening that enters into the Abandoned Lair's first floor.
Abandoned Lair 1st Floor
The first floor of the Abandoned Lair is free of Snakes. There are multiple rooms with beds and tables. There is also a room with a scroll detailing an unknown character's observations of the Lair.
In order to proceed further into the Lair, you must speak to Ko, who is in a room at the back of the Lair's first floor. Upon speaking to Ko, a player at level 20 or above will be given a mission to collect 100 Snake Venom. Upon completing this mission, you will be allowed to use the seal on the floor to access the Second Floor.
Abandoned Lair 2nd Floor
The Second Floor is filled with Venomous Snakes, which will add a Snake Poison affect when you get close enough to them. The effect will drain a small amount of health while active. The First room is similar to those from the floor above, with a bed and small desk. Moving to the left will lead you through a tunnel to a large square room filled with more snakes. Going further left will lead you through another tunnel, to a small room with a doorway.
Be warned, some snakes hide in these tunnels, using Cloak or Substitution is encouraged. In addition, you will be unable to cast any jutsu once entering the small room at the end of the tunnel.
The doorway will lead to a large maze of hallways, infested with Venomous Snakes. Upon exploring these hallways, you'll find large openings in the floor, walking into them will drop you down the the third floor of the Abandoned Lair. It is important to note that all of these floor holes lead to the same map, and there is no need to investigate each one.
Note: You may not be allowed to enter the doorway if you have been recently attacked, this includes having a Snake Poison affect. This also applies the the openings in the floor.
Abandoned Lair 3rd Floor
The Third Floor is free of any snakes, however all of the floor openings are traps that will kill the player. Upon exploring the Third Floor, you will again find Ko standing in front of a closed gate.
When engaged Ko will tell you that you are not ready for the Fourth Floor, and pushing further (Really?) will not help you. Telling him to take you back will teleport you to the bed on the Second Floor.