A great way of racking up the miles on a mountain bike without noticing the distance you are covering is to take part in a mountain bike orienteering event (although there is also lanequest, which can be done on road bikes).The concentration and adrenaline and racing against the clock and fellow competitors totally distracts from the distance you are covering.
There are two main types of mountain bike orienteering events the first is MBO score (also known as Trailquest or MTBO Score);
The score events are based on a time limit rather than distance to be covered. The idea is that you get a map (usually pre-marked Ordnance Survey Type) which has the control points marked on it. Each control point (also known as checkpoint) has a value, you decide which controls you will visit with the aim of collecting the most points within the time limit. The skill is to decide just which points are worth getting and in which order for your fitness level. If you go over the time limit you start loosing points! (you really don’t want that to happen). The time limits depends on the course organiser but usually the time limit is set between 2 and 5 hours. Control points are often marked with an orange and white orienteering flag (also known as a kite), beware though they are not always and it depends on the organiser (check when you enter the event). The controls are sometimes orienteering punch clips (pins which mark pattern on paper) or the new electronic punches (such as sportident).
The second format is MTBO (without the score on the end);
MTBO events are based on getting round a course in as quickly as possible. They are still map based events but use orienteering maps. These events are often held in forests or areas with good network of trails. There are often different levels of course so if you are a beginner don’t worry as you can choose a course that will be suitable to your fitness and map reading skills. The winner of these events is simply the quickest person to get round all the checkpoints marked on the course. Again this is measured by orienteering punch or electronic punches.
Apart from the obvious equipment such as bike and helmet etc. you may wish to use a mapboard, this aids navigation on the bike, practice first though before you hit the trails and never get distracted by looking at the map (I have seen someone run into a car whilst reading the map on the move).
Here is a list of Mountain Bike Orienteering Events