In reply to pasbury:
Carreg Lefain
Gwylwyr Quarry
These are the local crags near Nefyn. You'll find some bouldering in the quarry, and maybe some at the natural crag Lefain.
Declared interest: Duck Liver Pate in Gwylwyr is an old route of mine, from '97 I think. I'd like it to see some ascents, I think it's ***! ( well maybe one).
They're not right by the sea though.
There is a great bouldering wall down on a deserted stony beach at Craig Y Llam, if you go down the old quarry works incline from the clearing from where you would clamber down the steel hawser to access Fantan B, then scramble down to the little rocky cove between the Fantan B headland, and the main beach that stretches out towards Nant Gwtheyrn. I spent a lot of time there as a kid.
Access Craig Y Llam by turning down a farm track off the road from Nefyn just before reaching Llithfaen.
And if you want an adventure, and have ropes and partner, do Fantan B or Avernus on Trwyn Y Gorlech!