Mountain bike racing takes place in a variety of off road venues. Mountain biking can generally be broken down into multiple categories: cross-country, downhill, four cross, and freeride.
Cross-country races often use parkland, woodland and forestry sites, with the terrain chosen to incorporate climbs, descents and technical features. Looped courses are designed and built specifically for events by skilled course designers, with man-made technical features such as 'rock gardens' incorporated to increase the technical challenge.
Downhill courses are shorter point-to-point courses exploiting a venue's steep terrain, incorporating technical features such as rocks, tree roots, jumps and drop offs. Like cross country courses, these tracks are often created specifically for events or form part of a trail centre or bike park's established courses.
Four cross courses are, like downhill courses, built on steep terrain with manmade jumps, berms (banked corners) and other technical features. They're much shorter than downhill courses but wide enough for four riders to compete shoulder to shoulder.
Away from racing, the 'venue' for recreational mountain biking is huge; it's the great outdoors. Britain's network of bridleways and other legal rights of way extends to thousands of miles. For the adventurous type with a bike and an Ordnance Survey map, it's ripe for exploration. If however you like your riding more 'point and shoot', mountain bike trail centres are where it's at, with way-marked, graded routes, generally in forestry land, with all the amenities such as bike hire, bike wash, bike shop, cafe and changing facilities provided. Think of them as one stop shops for mountain bikers.