A classic dungeon! I enjoy the Lightning/Eel elements. The Secret Vault is a nice bonus goodie. The slots should be obvious to players who were paying attention, but it isn't overemphasized. (There's no indication of a secret door on the map, but I'm assuming there is one there.) The Shrine entrance is excellent! Good work!
Is 1.5 ft a conventional grid size for OSE? Just curious. :)