Just down the road from the main hospital is Park House, designed by the same architect as Hellingly Hospital, it's like a mini version. The admin buiding for Park House looks just like a smaller version of the main admin building down the road From what I can gather, it closed earlier than the hospital but I can't be sure as I am not the expert.
It's a bit harder to access but well worth the effort. One word of warning, there is a hole in the floor near the access point which goes down a MASSIVE distance. You would be dead if you blundered into it.