Accomodation for ca. 10-12 people wanted near London

Here's the scenario:

We're a social 6-a-side football team with a pool of about 20 regulars/semi regulars. We've done lots of parties, comedy nights, bonfire night meetups, etc. but now some of us are thinking of organising a day+night away. Not a whole weekend because some have kids or other commitments but maybe going somewhere early on a Saturday morning, spending the day walking in some nice scenery or doing another outdoor activity, then having food & drinks in a nice local pub and stay in a bunk house or something. If the accommodation allows for cooking, that's an option too (instead of a meal out).

I'm looking for ideas for
a) a location - scenic or interesting; not too far from London so it's worth going for just 1 night
b) an outdoor activity to do at or near that location
c) accommodation - what do I put into Google? Bunk house? Group accommodation? Anything else? (I'm being a bit thick but I've never had to organise anything like this.)

I'm grateful for any ideas and tips!
L_Q