The Temple of Bathrymrala

From publisher blurb:

Hex 24.26 -- the Temple of Bathrymrala, is the start of a new cluster of hexes. Two rivers join in this hex, creating a swamp in which can be found the remains on an ancient temple to Chaotic gods, now inhabited by a variety of creatures. The hex features five mini-dungeons that make up part of the partially flooded complex, new undead and plant creatures for use in Old School Essentials or other OSR-style games, and rules on creating and using summoning circles when summoning extra-planar beings.