I’d say take the bikes. Tourist offices hand out maps of local routes, which are waymarked. We stayed several times at the Yelloh site near Guilvinec and there’s a fair few off road routes, more gravelbikey verging to xc mtb. I’d call it relaxed biking I used to do with my kids with some nice and more interesting bits here and there (ride out along the granite cliffs to Point de Raz, say.
There’s plenty on line – google parcours vtt and where you’re interested in going. So randomly here’s a map with a few routes:
https://drive.google.com/file/d/1-mBU2P5KXUY5uMueU1Z_tdqDabpaDdAA/view
…got from here where there are a few more, from their events page
http://www.finisteretourisme.com/base-vtt-vallee-de-l-odet-quimper
…and here’s a few more from a site where people post routes. Can’t vouch for quality.
https://www.mountnpass.com/en/france/parcours-vtt/region-bretagne/finistere/concarneau/
There’s more of a hill at Locronan, I vaguely recall, with a few loops and bits and bobs, where I did my only ever clipped in carpark topple, to my kids great amusement.
The main draw for me is the Audierne thru Crozon coast for surf, but it’s a brilliant region to explore inland too.