Protips, especially for more immersive players:
1) I won't tell you too much about the underwater tour. You have to see it yourself. It's absolutely worth it.
Just so much: Just like the name indicates, it's under water. Not in a Jules Verne-style tunnel system made from Arcadia Asylum parts, but actually under water. As in you will get wet, and you'd better wear a wetsuit or swimwear plus diving gear.
In fact, it's best to take the Underwater Tour during an extra visit to Novale. And then I recommend you to change into your wetsuit or swimwear at home so you don't have to do that on the sim. Don't worry, you don't have to walk much to get to the start of the Underwater Tour.
2) When you take the kayak after the underwater tour, don't paddle back to the start of the underwater tour and get out of the kayak. Once you're out of the kayak, it's gone immediately, and there's no teleporter in sight. The only ways of getting away from there are by flying, teleporting via map (and you can't see much on the map), teleporting out of the sim altogether, taking the tour once more or swimming, and be it to wherever you can get another boat.
So when you're in the kayak, you'd better paddle somewhere that you know you can walk away from.