Living in London, I head for the Sussex coast. I discovered Brighton a few years' ago and went there regularly for days out, but it is very much 'London on sea'.
About four years' ago, I went to Hastings which I last saw as a child and my abiding memory was of seeing the finicular railway. Old Hastings is lovely and I had a fish bap from an award winning stallholder.
During this last heatwave, I went to Margate (another nostalgic visit), but it was grim to say the least. I walked from the station as far as the Turner gallery, but that part of Margate has a run down feel notwithstanding the smattering of vintage shops run by refugees from 'hipster' London. On my way, the train passed through Herne Bay and Whitley Bay and I wish now that I had gone to one of them instead.