Visited 07.0219
I parked up in Castallack and walked up the muddy bridle path to Castallack Round at SW44852539, at a right angle in the path. The grass in the field was short however there was no sign of a hut circle. On the OS Explorer map the hut circle is just north of the round in an impossibly overgrown area.
At the northern edge of the round this a pointed menhir wedged in the dyke and a Bullaun stone a few feet away. A Bullaun stone is a stone with a deep hemispheric depression which often collects water.
10 years since we visited, you have picked a much better time of year to go. Great to see the stone and the basin.