Another one for Manchester Mountain Bikers here- it’s all organised through a meet-up website so if you’re nervous about meeting new people (and let’s face it, who isn’t?) you can peruse the website, check out forthcoming rides and current members etc from the comfort of your lounge first.
There seems to be plenty of female-orientated stuff organised as well.
Everything that everyone has mentioned above looks like top fun though so I’m sure you can just take your pick really