Center Parcs certainly seems to have a decent amount of wildlife on site. It is actively monitored for a number of groups of animals, and I think there is active management for wildlife. Certainly, it frequently appears in the Notts Birders annual reports.
Both
Rufford CP and
Sherwood Pines CP are within a short (walkable distance). Slightly further afield are
Clumber (NT),
Sherwood Forest (The Birklands) and Budby Heath. I've linked these to the Notts Birders site guides.
These sites are good for birds, great for fungi, but its still a bit cool up in Notts for many insects and spring flowers yet.
HTH,
poschiavanus