Jules Verne Lodge, Underwater "Hotel" 

This underwater habitat is located in a lagoon on Key Largo, Florida, USA, reached via the Overseas Highway, A1A.
Once a research lab, it has since been renovated into a quaint 2 bedroom 'hotel' for overnight stays and daytime visits by reservation only. They have a full support staff and even "room service" where they will bring down your meal ordered topside.
You can dive the lagoon before entering the Habitat, and then enjoy some leisurely time in the undersea environment with its 42" picture windows looking out into the lagoon.
There is even decent WiFi down below, so you can still communicate with you friends ashore via Skype and other social media.