Depends on whether you value solitude or not. Suffolk coast is pretty good for windswept beaches. Same up the coast in Norfolk.
But for a solo traveller, and if you want some variety, it has to be London. And I'd concentrate on the bits east of the West End. Soho, Knightsbridge etc have all had their day.
Holborn, Farringdon, Smithfield, Clerkenwell, Shoreditch, The City and those environs are great for walking around and exploring. As much history, culture, and architecture as you'd want to take in. Tate Modern is still amazing, and free to get in. The whole area is walkable, and dead quiet at the weekends.
Not much in the way of parks, but so fucking what. You can walk along the riverside, get a boat to Canary Wharf or Greenwich (another great spot.)
If you can splash out a bit, there are now some excellent hotels in the EC2 area. There didn't used to be any. And as far as bars, cafes and restaurants go, it's easily now the best neighbourhood in London for choice.