Carbis Bay has its own rail station, on the St Ives branch line from St Erth to St Ives. St Erth is on the main line from Penzance to Plymouth and there are regular trains but check out those that stop at Carbis Bay. Borthalan House is a short walk from the station but on a fairly steep hill.
Follow the main route A30 to St Ives, leave the A30 at the sign-post - A3074 to St Ives. Follow the A3074, through the village of Lelant, then drive into Carbis Bay. Take the third turning on the right onto Boskerris Road, follow the road down the hill and take the first left, Borthalan House is a hundred metres on the left.