This is cargo hold number 7. Savannah was built as a hybrid cargo/passenger/demonstration ship, the compromises of her design included smaller cargo holds than on a conventional cargo ship of her size.
The automated hatches can be seen above. During operation this would have been full of goods being transported. Now there are just some mooring lines flaked out on the deck.
In the photo to the right you cans see the cargo booms used to load the ship and the hatch covers from deck. Some additional difficult compromises to the cargo handling from her complicated mission can be seen in the rake of the masts chosen for their sleek look that limited the range of lightweight cargo booms. The swimming pool limited easy access to the hold below it (access only from the sides). Finally, the weight of the reactor limited its fore and aft position in the ship, but it still needed overhead access for fueling operations. This limited the use of the space above the reactor.