I have worked near here, at Brighton General Hospital, for many years. During my lunch breaks I would go for walks and I found this passage, that goes under the race course, leading to Whitehawk area of Brighton. The path takes you to the other side of the race course stands, where there is plenty of wild life, including butterflies. There are also some great views over Whitehawk itself, which I found to be of interest.
You are looking for a black nano just above the start of the passage. However, please take care, especially if you have children with you, as there is potential for falling onto concrete. Although there are railings to protect you.
Due to the location of the cache muggles may appear without much warning. However, I have tried to place the cache in a place where you are hidden.
Parking can be found at the Garden Centre.