There are public WCs between the race hub and the cafe in the centre of the park. There are also WCs in the cafe.
There are also WCs at the main College Road entrance to the park. The main gate to the park is opposite Dulwich Picture Gallery.
After you enter the park from the main gate, turn left just before you join the main carriageway which encircles the park. The WCs are about 50 metres up the path. These tend to be less busy than the other WCs. If these are busy there is another WC in the Francis Peeke centre which is a bit further along, next to the car park