The Benthic Academy: An Undersea Ruin (Patreon)

NOTE: There are two versions of this map: one with air pockets in a few rooms and one without.

When I draw a ruin, I like to trash the place. I don't want it to just be a building with holes in the walls, I want it to look like a hotel room the Rolling Stones spent the night in in 1976.

In this particular map, however, some parts are less trashed than others. That's because the Benthic Academy is a college of magic-- or, at least, it was until whatever disaster swept it under the waves. Unlike most places, the academy has magical wards holding some of it together, particularly the library (on the right), the faculty rooms (bottom center), and the dean's residence (upper left).

The wards were meant to prevent cracked walls, broken windows and leaks, but they've done such a great job that, even after years underwater, a lot of the academy is still in one piece. Depending on which version of the map you use, they may have even caused a few of the upper-level rooms to retain air pockets.

If you might be using this map, I've got a few suggestions. First, I'd recommend considering your party's underwater capabilities when planning encounters. Keep in mind that most melee weapons roll with disadvantage underwater. And, even if your players stop to re-equip themselves at Tridents-R-Us, you may need to consider how dependent they are on any magic weapons they won't be using. If that Hammer of Hit Point Obliteration is doing a lot of work, you may want to dial the enemies back a little. Also, remember that Lightning Bolt and Fireball aren't really on the menu anymore.

Second, I'd start the party out on the roof level. Since they're swimming down into this, that's the first thing they'll see.

And finally, if the spellcasting PCs can't cast Water Breathing enough times to  get the whole party down there, just put a few potions of water breathing into the loot of the adventure before this one. Don't worry, handing out suspiciously convenient water breathing potions before an underwater quest is an ancient DM tradition.

Next up, I'll be drawing another map from the Black Loch: the surface entrance. This isn't a stairway, it's a series of waterfalls, and it's probably the quickest way into the Underdark from the surface. Is it the safest way? Probably not, but that's your party's problem. Also, since this entrance presumably leads down from a river on the surface, it allows for the possibility of traveling to the Underdark accidentally. And the best part: it's one-way.

Anyway, I'm gonna start sketching that out. Let me know what you think of the Benthic Academy!

There's an annotated version of this map and DM notes available to patrons.