This cache is near the site of a 1883 built water tower of the former Foredown Isolation Hospital. In 1991 it was transformed into camera obscura, one of 2 remaining in the the southeast.
A public footpath runs past the building and along the south downs, so its the perfect place to begin your walk and you can even collect a few more caches on route.
You are looking for a magnetised bison tube containing a log book, so bring your own pen/pencil. You might only need to unscrew it to access the log but you can remove completely if needed.