The coast path won’t be a good idea in summer, that’s very much a locals-only treat for the off-season.
The route in STW wasn’t bad, but does ride around the better stuff. Then again all the better stuff is unmarked, and prone to being rebuilt between printing and riding, so I can understand why they stuck to legal rights of way. The mine mentioned above is Poldice Valley, and Carn Marth/Brae over Redruth have good tech descents on, both of which you’ll ride past.
If you want a quick ride and you didn’t take a bike then Cardinham has a solid 10k waymarked loop and bike hire (via trail munki, check they’re actually open), so is definitely the best option for a quick ride. Grab the pork ciabatta from the cafe to refuel.