Visited 12.4.10. (on way to the lovely Sennen Cove)
The stone is not visible from the road. Park at the 'First and Last' pub - next to the church.
Opposite the church is a field with a row of bungalows running alongside it. Walk down the lane which runs in front of the bungalows until you come to a farm gate. Over the gate and follow the very muddy track to the large cow sheds. Just before the cow shed the stone is visible to the left - behind the shed. If you want a closer look you will need to climb over the next gate and walk around to the far side of the cow sheds. The stone appears to be about 7/8ft tall.
There is no public access to this site but as there was no one about I took a chance!
Interestingly, one of the bungalows has errected their very own standing stone in their front garden!
From opposite Sennen Church (with its couple of fine old crosses), a private road runs back toward the farm buildings. The footpath is shown as going up to the shed, but I'm not sure where it goes from there. I ventured over the locked gate, and around the back of the shed, startling a large fox in the process.
The stone, visible from the road when the foliage is low, is built into the field boundary wall, is covered in lichen, and I'd guess stands approx 3-4 metres tall. Being on private land, permission should really be sought, but there was no-one around during my brief visit, other than a herd of cows in the neighbouring field.