So there's this German guy by the name of Talhoffer. He wrote a really famous book on medieval fighting techniques that's simply called the Fechtbucher, or as it's translated "Fightbook". He actually wrote several of them, but the one I'm going to talk about was written in 1459. In it he illustrates different fighting techniques for just about every kind of personal combat you can imagine. He also illustrates a few different siege machines for good measure.
However, what caught my ey most of all was this particular illustration:
At first glance it appears to be some sort of weird hybrid between an elephant and a human, i.e. "Elephant Man". Perfect for a weird and unsightly creature for your players to run into in their journeys and adventurings.
It's actually a design for a diving suit. The long nose is actually a tube that would run above the sufarce of the water and then attach to another tube, which would then be attached to a set of bellows. The bellows would be pumped furiously to allow the diver to breathe while underwater.
Not too long ago the National Geographic channel ran a special on Talhoffer and the Fightbook, and one of the things they did was to test the dive suit out. Surprisingly enough, it worked perfectly, though I don't know if they used modern materials or period accurate materials in it's construction.
If you want to look at the Fightbook, you can as the whole thing is online in all it's lavish detail.