Though Brighton, and in fact the entire Sussex coast, has a pebble shoreline (which is natural by the way), once the low tide recedes out far enough, a layer of sand is revealed. This layer is largely flat for a fair old distance out to sea so naturally a low tide event at sunset brings the locals out in their droves.
As the water recedes further and further, it is an opportunity to walk barefoot along the exposed sand and sometimes the water recedes so far out that you can walk beneath the superstructure of Brighton Pier and wade close to the ruined shell of the West Pier. It is a precious moment to relax and soak in an atmosphere that feels wholly unique to Brighton.