Check this thing out. The SeaOrbiter is French (harking back to 20,000 Leagues Under The Sea) and has twelve decks, six of which will be below sea level. The 22 person ocean laboratory will go out on three to six month voyages during which it will conduct oceanographic experiments and also psychological and physiological experiments set up by NASA.
A fleet of five is planned. We know little more about the oceans of our own world than we know about space, so I'm actually quite psyched about this.