If coming from almost anywhere in the country, turn west onto the A30 at Exeter towards Cornwall. After quite a while turn right at the sign for St. Ives.
Follow the road to St Ives and after several small villages you will get to St Ives. Keep on the through road up the hill at the big Harbour Hotel. Follow the road up to the top, past a large car park over one roundabout and keep going till you come down a hill to a mini roundabout. Turn left, then straight away right at the next mini roundabout - up the hill - Carnellis road. Follow this road for a while, then the road will bend sharply left and you will see the sea at the bottom of a steep hill. Hooray! Head to the bottom of the hill and turn left before it bends to the right. The house is about half way along the road on the left. It is called 'Tresillian'.
There is a large parking space in front of the house for 2 cars (1 must be small/medium sized). Cars should not overhang the pavement too much.
Alternatively take the train to St Erth (on the main London - Penzance line), from which you can either get a taxi or take one of the most scenic branch lines in England, to St Ives.