Decrepit Solitude is a Single Player level in Q2. This level has the same geometry as Entering Eternity, most of the differences besides texturing are in regards to Enemy and Ammo placement. This level also the same geometry as Caliginous Minaret/Underworld Excursion, though placement of Ammo and Weapons is entirely different.
Turn left to look down the corridor. Kill the Grunt in the doorway to the right, then return to the corridor. Kill the Grunt in the room on the opposite side of the corridor, then collect the Rockets and return to the corridor. Continue to the next two doorways while collecting the Rockets. Kill the 2 Grunts in the room to the left, then collect the Rockets and return to the corridor. Cross the corridor to the other room and kill the Grunt. Collect the Rockets and Grenade Launcher. The corridor outside bends to meet up with the doorway on the left. Before returning to the corridor, go into the room to the right and kill the 2 Grunts. Continue down the corridor to the end while killing the Grunt. Before turning left to continue following the hallway, kill the Knight and Grunt in the room to the right. Kill the Grunt before proceeding down the corridor to a door on the left side. Kill the 3 Grunts and an Ogre while collecting the 2 Cells, then return to the corridor. Continue to a doorway on the right. Kill the 2 Grunts and the Knight before returning to the main corridor. Continue down to the next doorway on the right. Kill the Grunt and collect the Rockets, then return to the corridor. Continue to the end of the corridor and turn left. Kill the 3 Ogres, 3 Rottweilers, and a Spawn while collecting the Thunderbolt. Enter the doorway on the far left and kill the Knight in the final room.