The Grisley Grotto is a small map, but has a high monster density.
After starting, the first door leads to a downward spiral staircase, with ogres attacking from above, and a scrag approaching. Going down and through the door leads to a wide open watery area, and a biosuit if you need to remain underwater for a while.
Dive in, and head down towards the bubbles. Enter the building and surface. You can collect the super-nailgun, defeat the two ogres and proceed down the corridor. You will encounter two knights. In the building leading to the lift, there is a bit of water hiding an ogre. You can shoot it at before the floor raises if desired. The lift is at the back, but two knights will try attacking from the side.
When you reach the top, three knights will rush to attack. Defeat them and head left to press the button. This opens the door leading to the silver key, but also spawns scrags. When you enter the door to collect the silver key, additional scrags will spawn in the main area. However, the silver key gate is ahead, just below a water entrance.
Go through the silver gate; you can take a right turn to press a floor button to reveal armor if required. Otherwise, take a left turn to reach a slime pit and a lift. There's nothing in the slime pit, thus you should proceed up the lift.
The next room contains five floor buttons, used to reach a secret exit if desired. The regular exit is located through the path leading left, through the door, and across the bridge.
- At the start, you should see two buttons in the downward spiral stair case. Shoot them to lower a lift and get access to secret armor.
- When you enter the watery area, swim down, and to the right. There should be a small cave where you can surface to collect 10 rockets.
- You can find five floor buttons past the silver gate. Walking on them triggers a nailgun trap, but stepping on all five will open the two side doors in the same room. Enter each side door, and press the button in the alcove. When you press two, you will be alerted about a secret cave. This cave is found in the water area, on the opposide side of the first entrance, contains a grenade launcher, and allows you to exit to Ziggurat Vertigo.
Items of note:
- Double barrel shotgun at the starting area.
- Nailgun past the silver gate, near the slime pit.
- Super nailgun at its normal position, the water-entrance to the silver key area.
- Grenade launcher near the exit, as well as in the regular position in the secret exit.
- Rocket launcher replaces the silver key.
- Pentagram of protection past the lift
- Ring of shadows complements the grenade launcher in the third secret.
- At the starting area
- Near the exit (backup for the grenade launcher)
- Near the pentagram of protection
- At the entrance to the silver key area, in the two structures (super nailgun ahead)
- At the silver key gate (backup if you want to reach the nailgun or yellow armor)
- Near the rocket launcher
- At the slime pit, facing the nailgun
- Above the slime pit, facing the lift
On Hard difficulty, there are 59 monsters. A glitch may occur where you can only kill 58 of them; to avoid this, approach the silver gate before collecting the key, and kill the monsters guarding the gate.