We visit Seacliff Beach quite regularly. It is only half an hour drive from Edinburgh, few miles behind North Berwick, just few hundreds meters from scenic Tantallon Castle. It is a beautiful beach with golden sand flanked from western side with cliff face. There is a small rocky hill on that side, which offers amazing view to Tantallon Castle to the left and beautiful Bass Rock island straight ahead. Just below that hill there is a strange trianglular dock (actually, I have no idea how to call it) with vertical walls, so be careful not to fall there. On the eastern side, the beach ends with a rocky peninsula/tidal island, with the small, concrete cross at the tip.
We love that beach less for its sand and water and more for huge number of tidal pools in these rocky formations on both sides of the beach, which Annie loves to explore looking for stranded sea creatures. Also, the view to Bass Rock is just amazing. Over the eastern side of the beach, just behind the main car park, there is another castle located (ruins of it really) called Auldhame Castle.
Seacliff is apparently privately owned (or maybe land around it is privately owned), so to get there, you need to pay £3 at the automatic gate (accepts coins only). Car park is quite big, but the road leading to it is full of holes, so I would recommend driving with care.