Spider Nest sub-location (this location is unique to Remixed Pixel Dungeon) was firstly added in remix.19 update.
Fellow heroes can enter the spider nest from level 5 by equipping the Spider Charm and going down, if the Spider Charm is not equipped, then the hero will appear in prison levels as usually. Now hero can just go to regular downstairs on level 5.
Nest layout differs much from your usual floor layout, for example, there are no doors, but plenty of plants growing everywhere. Mob spawning logic is also different, instead of spawning mobs in random unseen parts of the location, all spiders come from eggs or nests. So if you don't want to get overrun by hordes of spiders, then it's in your interest to try to destroy the nests first…
Down there the hero will meet… well… a hell of a lot of spiders.
Spider Nest floors tiles and mobs designed by Pavel Provotorov.