Random Janitor curious about forbidden bathroom opens portal and lands into an interdimensional, intergalactic gladiator arena run by corporate space business aliens for lolz and betting.

I thought perhaps someone here might have an idea. The story starts off with a janitor in a corporate office building. There is a bathroom on the executive floor that is the only place he is not allowed to clean. Bored and with a "no one is here, so why shouldn't I take a peak" attitude, he gets the unusual gold key, and opens the door. The next thing he knows, he is in the desert(I think) and being attacked by a lizard man. He then goes on an adventure across multiple worlds using the golden key to open doors as portals(If I recall correctly). He finds out he has stumbled into some sorta interdimensional gladiator arena run by evil space business aliens. In one of the realms they(he meets others) sail across a sea of gravity altering flowers on strange ships, and in another they enter this strange city that while on the surface seems idyllic, is infected by some sort of hive mind parasite that lives underneath the city. Conflict with other gladiators happens regularly.

It is a very short book and that's all I can really remember. I found it on a shelf and read it in one sitting like 15 years ago and every now and then it pops into my head. It is a really fun little adventure story and I wish I could remember it. Any ideas?