Withdean Sports Complex Training Centre is a small building next to the lower car park. If you are at the main entrance, walk down the path past the pub, and the Training Centre is on the right.
There is plenty of free parking in the complex car parks. The lower car park is directly outside the training centre. Alternatively, the nearest train station is Preston Park and there are several buses that stop on London Road (5 min walk under the railway bridge) or the no 27 stops directly outside the complex.