(continuing my goal of using every book as a D&D sourcebook)
The Riddle of the Sands is is a pre-World War I British spy adventure, written by a real British spy who was later EXECUTED FOR TREASON. I think this adds a lot of authority to a book. Imagine if Naomi Novik, author of the Temeraire novels, died by FALLING OFF A DRAGON. That would give her a little something called AUTHENTICITY.
The characters in The Riddle of the Sands spend a lot of time poking around the German coast in boats, and there are a lot of details about Admiralty charts and tide tables. Some sailing exploits, and sights, are only possible at high tide. For instance, there’s an abandoned church on an island: at high tide, the island is underwater and the church can be seen sitting on the surface of the water.
Imagine the temple crypt below such a church. A macguffin entombed in the deepest part of the crypt might only be accessible at low tide, for, say, an hour; soon afterwards, water would start flowing in, giving the DM a great excuse for the classic rooms-filling-with-water hazard. On Earth, it takes about 6 hours for a tide to come in; so in a reasonably-sized dungeon, the PCs won’t be in danger of drowning unless they get caught in a trap or there is some sort of delaying terrain. This dungeon should probably have both.
What monsters would be in such a dungeon? In order for water to flow into the crypt, there must be an outlet to the sea somewhere. Mermen and other aquatic creatures can definitely be hanging out in whatever portion of the crypt is currently underwater.
The currently-above-water part of the crypt is more difficult. It must only be inhabited with amphibious creatures – which, luckily, includes undead, the most obvious dwellers in a church crypt. Imagine a skeleton which has spent half its time underwater for hundreds of years. It and its axe would be trailing weeds and slime; it might or might not be part coral (depending on how much you like The Tempest: does that sea change stuff actually happen?); and it would undoubtedly have something gross in its eye socket, skull or rib cage: a dead fish or scuttling crab.
The rest of the dungeon would be pretty unpleasant too: the church itself, up to a few feet up the walls, would be coated with weeds and slime, and paved with muck and stinking fish. Every level down would be successively more unpleasant.
Tags: everybook
Hmm, fun terrain/ideas to use in encounters:
1. Slime: Simple terrain that requires an acrobatics check to cross or you fall prone!
2. Water: As rooms begin to fill with water, areas might become submerged, requiring swim checks and the like.
3. Rooms that Change: Maybe the group has an encounter in a room while at low tide and it’s a relatively normal dungeon but the next time around it’s partially submerged and inhabited by angry mercreatures! Maybe what was once a series of platforms is now a group of island like areas. What was once a trap that could easily be disabled by pulling a lever on the ground floor now means holding your breath and swimming in the dark while enemies attack you on all sides. Stuff like that!
4. Stench: Rotting fish and weeds could attack fortitude every round or some such and give negatives to attacks!
5. Puzzles: There could be some interesting puzzles that involve doing something at low tide and then waiting for high tide to swim up to a higher level without the benefit of a fly spell or something similar.
Right! I have access to every trick from those water-table-changing levels of Mario 64 and Ocarina of Time. Those horrible, horrible levels.