Back in the 90's I did a lot of NATRC rides. I even sponsored a ride for 6 years. ( Which is a lot of work)
The challenges at any given NATRC ride will depend on the judge that is there and what natural obsticles can be found. NATRC really encourages using natural obsticles vs man made. You can expect to be judged on your mount. Your horse needs to stand still while you get into the saddle. If water is available. If will often be used an obsticle. as in a creek crossing, we even once had to cross a lake about belly deep. Steep up and downhill grades are common judging areas. and of course things such as side passing over to tie a ribbon on a branch, backing between two trees, crossing blow down logs on the trail can all be expected.
Almost all NATRC rides involve camping and staying for the weekend. They do offer a single day event. But the cost to put on an event and the travel cost to attend just don't support having one day rides. So almost all rides are two day events.
The rules are defined to make the event as equal as possible. All riders must complete the ride in the same amount of time, Too fast or too slow and you are out of the game. Any forward progress down the trail must be done while riding, No running alongside your horse to save him. All horses must be kept in the same manner. If stalled, All horses must have stalls, Hence most NATRC rides keep the horses tied over night. It's not fair for one horse to have a nice corral to stretch in and somebody elses horse needs to be tied to the trailer because they can't afford a corral.
Check out their website. They are a lot of fun