London, the Presbyterate, the Khanate, Khan’s Shadow, the New Sequence and even the Iron Republic have all concluded that there’s nothing of any importance under the Zee, and they’ve all agreed to leave it well alone. That means the places below the waves are off limits to you, too.
The Agreement About Nothing of Consequence, signed in 1896 but circumvented by enterprising zailors almost immediately, is a treaty between the various nations of the Unterzee to ban all exploration of the Unterzee's depths as well as research and construction of zubmarines.
Prior to the Agreement, London's Admiralty conducted its zubmarine research at Station III; the Khanate's zubmarine research base is unknown, but some scientists associated with the project later took up residence at Khan's Shadow.
Ambitious zee-captains looking to circumvent the ban on zubmarines have been suggested to seek out the Fierce Philanthropist at Port Carnelian.