There's something mindnumbingly monotonous and just a little masochistic in riding round and round in circles around the same track for hours.
Lap racing: 5, 6, 10, 12, 24 hour events where you try ride as many laps as possible in the allocated time.
But there's nothing boring in riding the same track if it's sufficiently technical. Bonus points if there's night-laps involved :) The more you ride the difficult parts, the easier they become. That gnarly downhill on the first lap becomes a huge-grin downhill on the 5th lap - and maybe taken slightly too fast on the second-to-last lap :) That rocks that you walked on the first lap become ridable after the third try, and finally after the fifth lap you were in the right gear for that steep climbie right after the steep turn.
Lap racing is as hard or easy as you make it. Which usually make them very hard. You've got say 6 hours to ride as many laps as you can manage - or as far as you want. It's up to you to decide if you're up for another lap, or if you'd rather take a break and have lunch. You decide if you want to aim for a total of say 80 kays for the day, or if you want to see if you could ride nonstop for all 6 hours. You can find out where the boundaries are without any risk - if you entered an ultra marathon and 3/4 of the way find that there's no more energy, you still have to get yourself to the finish. Not so with lap racing - if you're at the end of your energy, you can simply stop. Safe.
If you're slow and used to arriving at the finish when the marshalls have packed up the tables, and used to searching for the timekeeper to take your time, it's great to finish with a crowd to cheer you in :)
A big bonus is that you get to see the fast people in action. On mountain bike marathons you'd start way after the big guns, and by the time you finish, they're already home and showered. On lap races, there's a good chance of being lapped by the faster okes - so you can see them clearing the obstacles, check out their lines and try it yourself next time.
There's usually a great vibe at these events. Teams (riding in relay format) vary from very social (taking beers with on the laps) to very competitive, and it's great coming in from a lap and see the festivities going on in the different gazebos. Slow and fast people all in the same team, and all can have fun. It's usually much more spectator-friendly than marathons, cos supporters can see their heroes in action. And have a chat inbetween. Or bring food :) and carrot cake :D
There's a 24 hour first weekend in December at Rietvlei. Anyone wants to join me for a team of soloists?