Nikonos IV with the standard 35mm lens really is a good idea, its reasonably compact, the lens works both above and underwater and its tough as hell and is actually pretty decent.
I used a 35mm Nikonos IVa for years with the 35mm lens. It's very sharp, built like a tank but handible. I used it scuba diving, snorkeling, white water rafting, para sailing, on the sand, in the rain etc. Here're some shots. Check the scuba albums. https://www.flickr.com/photos/alanklein2000/albums
If you consider warfare an adventure, that's what the Kodak Signet 35 was built for. (Korean war.) Great lens with a so-so shutter that is easier to work on than most shutters. Drag it through the mud and then clean it if it stops working. It's a rangefinder and the back comes off in case you drop the camera when loading film. eg. while dodging bullets. The controls are designed to enable the user to operate it while wearing gloves.