I am not a Marine, however, I caution you that thinking "learning land nav would be cool" before you go to flight school is going to lead to you being one very unhappy camper. If you want to join the Marine Corps your main motivation should be becoming an officer of Marines. The TBS experience is all about the ground pounders and it tends to deify infantry officers. A few of my friends who went there with guaranteed aviation slots almost gave them up to put their names in the MOS lottery for an infantry slot. They didn't do it and in retrospect were quite happy they did not, (flight school is a lot of fun), but some of these guys were Embry Riddle graduates who were absolute aviation whores. That should give you some idea of where the focus is at TBS and the level of kool-aid drinking that occurs there.
I am not trying to dissuade you from going down the green (dark) side, however, if you do, do so knowing that it is way more than a show and tell exposure session to the infantry side of the house. There are a lot of advantages to the way the Marine Corps does it, no question. For starters they train every officer to lead troops on a basic level which emphasizes the leader first, aviator second mentality. The stash jobs that Marines have pre-API tend to reflect this focus on leadership.
In contrast the Navy drops newly minted ensigns right into flight school, an evolution which done properly resembles a well funded fraternity party. If you get a stash job it is likely that it will be handing out towels at the pool or counting laps at the mile swim, not exactly jobs that require a college degree or any leadership ability at all. The first 18-36 months of a Navy pilot's career is focused on turning him into an aviator. It's only after the Navy makes an officer a pilot that they entrust them with troops, and by the way, there is little formal training on how to lead those troops. It is expected that through exposure and observation you will pick it up along the way. The process generally works, but it is hard to say that the pipeline reflects a focus of leader first, aviator second.
If you want to be a Marine, do so because you genuinely want to be a Marine officer and lead Marines. Do not do it if you just want to see some cool stuff before flight school. The Navy has been a great fit for me, and the Marine Corps has suited a lot of my friends just fine. It's all about finding the right fit for you and ultimately you will be happy with your decision.