This is Doors to the Unknown (1996), an anthology of four kind-of connected adventures by Bill Slavicsek. Though there would be more Planescape adventures, this is the last one in the module format. As you might guess from the title, each scenario starts with a door, from Sigil to someplace else, and this feels like a nice theme to end the modules on.

These are a little unusual for Planescape adventures. They all start as sets of plotted encounters, which is pretty familiar territory, but then they all open up into small planar sandboxes where players can explore as they wish. This works because all the sandbox locations are fairly isolated. And also weird. One takes place in a junkyard. Another plays out in hyper-reality, where reality is more real than where the players come from (and things like damage and experience points are all doubled). There is an interconnected mystery concerning the four doors – players can only enter the fourth after solving the first three. There, they confront a rather cleverly conceived villain – a creature from hyper-reality that had decided to become a god in our lower reality by shedding his skin and bones. Like I said, weird.

The four scenarios are designed to be sprinkled into an ongoing campaign, which is something I appreciate (The Great Modron March also does this and it is probably possible to merge it with this with satisfying results). If there is a downside, it is that Doors to the Unknown feels like the start of something bigger that never manifested in the line. Its a shame Slavicsek never returned to pen more Planescape material.

There is some very nice art by Tony DiTerlizzi and Adam Rex here, too. Love the retriever in particular.