Willing to travel how far?
City or seaside?
London, especially when weather isn't so nice. Love the place for short brakes. Great public transport and so much to do and see.
£500? Go abroad!
Oi!
Bristol has a great music scene(everything from metal->ska->pop->DnB), a nice free museum, good shopping and is cheap. Few natural beauty spots (eg clifton suspension bridge), and lots of history to explore too.
Or hit Falmouth for a quieter holiday, it's very pretty and there are cool boat tours, but they're better when it's warm!