Recently, I soloed my way through Apartment 71 (30 pages) an adventure for Call of Cthulhu. I soloed this with the Plot Unfolding Machine (same place). I did use the four PCs that are provided: bookstore owner, law student, military police officer, and an author. These four were at a condo association meeting (this qualifies for horror) when they were notified of a problem with one of the units. The groundskeeper gives them some additional information and leads them to a storage room. They find some clues and a key and move on towards apartment 71. When they get to that floor they meet Jaime and his cat and get more information. The PCs use the key and enter the apartment and the cat leads the way.

So, the apartment ends up being a pocket dimension (I love pocket dimensions). Each room is stuck in a different decade and the PCs are stuck here (the door is gone). The PCs explore and gather more information. In one room they find a depressed woman and in another room they find a man suffering from drug withdrawal. Things really get interesting in the master bedroom. In here they find a vain actress (Alma) performing a ritual. The ritual was supposed to make her beautiful again. Instead, the pocket dimension was created and time stopped inside it (so, her appearance will not change). The current ritual creates a barrier so that she is protected. On the floor the PCs see the rune circle. There are marble sized crystals which have been precisely place on the rune circle. The PCs can not get to her or the runes, but the cat can. It smacks a crystal and it rolls to the far side of the room. The magic barrier comes down, the pocket dimension fractures, and Alma screams. The PCs decide to make a run for it. They have trouble finding the exit, but the cat helps them. So, the PCs and cat do escape. They forget about the two lost tenants who are still in there. They are now still in there along with Alma, in the fractured pocket dimension. The PCs did lose some sanity, but earned some experience. The complaints have stopped concerning that apartment so the condo association is happy about that.

Give this a try!