Wytham Wood, Oxford
This wonderful old broad-leaved wood West of the ring-road is owned by the university & you're not allowed in without a walking permit (which is hard to obtain). However, they regularly ask for volunteers on projects & experiments such as the annual badger census (middle of May) so if you want to do something really different while in Oxford (and you are a wildlife-loving insomniac), this could be it! See http://www.wildcru.org. Wytham is worth visiting anyway for its super pub, the White Hart.