Fortunately, there is a means of traveling provided if the players are able to role-play well. The book does a really good job of introducing underwater adventure, and I would recommend it for those who may want to go into a larger scale underwater campaign. I think it would make a good diversion and if it goes over well with your players, a whole new direction to play. This module focuses on role-playing, puzzles, challenges, and a little bit of combat. The players are not going to encounter NPCs out to kill them or rule the world.
Foes are mostly in the form of monsters from old time periods.
Being an adventure about time, there is of course a wealth of new information on such within. Characters will find themselves contending against temporal skids, time traps, and other interesting ideas. The book contains several new spells, all based on the manipulation of time. There is also a new clerical domain, Time. New monsters are introduced, but they are thrown in about the book rather than detailed in an appendix.