According to the ship's website, the SS Galaxy - The Queen of the Sagittarian Sea - was quite the attraction in her heyday: "With over 650 meters in length, 110 meters beam, and 8 decks of living and leisure space, the SS Galaxy is the largest single-build and the most exciting attraction in Second Life today." An impressive build that spans a full three sims, the Galaxy was created in 2007 and once featured a full staff, over 100 rooms available for rental, a shopping mall, a variety of activities and regularly scheduled events, and even "cruises". (While the ship does not move, the staff would set up monthly "Port of Call" excursions via teleport exchanges.)
Unfortunately, the Galaxy is no longer a working vessel with on-board rentals and scheduled events. In May of 2015, for a variety of reasons, it shut down, but in August of that same year, Linden Lab stepped in and reopened the cruise ship as a museum of sorts. A team of Lindens and Moles created a "Preservation Society" and added some new attractions for visitors: a water slide (see final picture, below), swan boats, a hot air balloon tour, a bowling alley, and even a working movie theatre. Large wall maps located throughout the ship will give specific and direct landmarks to the various attractions.
Many of the original areas have been carefully preserved, such as the Wedding Chapel and Reception Hall, pictured above, or the charming Bamboo Garden Japanese Restaurant, pictured below. There are a couple of art galleries to visit, and a nicely-appointed spa area. See if you can spot Bob the Boulder, a place where the sea floor actually juts up into the ship!
Located right off of the Blake Sea, the SS Galaxy is easy to reach by boat from the Mainland. Although there are no rezzing areas on the ship itself, a tiny nearby island offers a free sailboat rezzer. You can also sit around a fire on the island and watch the hourly fireworks over the Galaxy, float around in Galaxy life preservers, or play 7Seas fishing from the island dock. Or, head back over to the Galaxy to explore some more! (I highly recommend the water slide, myself.) With a ship that spans three full sims, you're sure to find some fun onboard. Enjoy!