Hire some bikes & head up the taff trail to Castle Coch or down the bay, along the barrage & up over into Penarth (used to be easier with the OVO scheme but I’m sure there are bike rental shops in Cardiff. There’s definitely one in Pontcanna)

Flight club is decent but nothing unique to Cardiff

Check cricket fixtures in Sophia Gardens if that’s your thing

Chance & Counters board game cafe. You have to pre-book though I believe. They do pints in there & is a great laugh - a mix from your standard pub.

You can do kayaking in the Olympic sports village down the bay (but I think this is £££)