on the stone circle front Men-an-Tol is my fave, its just north of Penzance.. IIRC theres another ancient thing on the way thats a big slab suspended, perfectly for comedy strong-man pics.
have done heligan before, its ok.. bit of a hike up from penznace. i’d say the monkey sanctuary in looe, but thats a bit far as well.
tbh eden project seems pricey, but when the mrs and i were down there earlier this year (stayed in mullion) we realised that although we’d paid at least a tenner for various places we didn’t spend anywhere near as long there as we did in eden.
and as martinhutch said, trebah is really good. we did two or three national trust places too. theres one near penzance with a walled garden.
one thing thats not too far is the cafe at godrevy, nice localtion right above hte beach and theres the lighthouse nearby. (drive to hayle, turn towards the coast at the double roundabout by lidl and keep going, its next to a surf school..)
beach recommendation, poldhu cove. really good little beach. swim/surf/lifeguards/loo’s and good parking.
stayed right in the heart of st ives before, always good. stayed in mousehole before as well. st ives gets stupid busy, but now kids are back at school won’t be so bad.