A short boat trip at low tide takes you across to Carn Near. So called due to it being the closest point to St Mary's. From here you're about 10 minutes or so walk to the Tresco Gardens. We were hungry and as we'd gone on the 12.15 boat we headed instead up the west side of the island to New Grimsby for lunch at the New Inn, taking in the views along the way across Tresco Channel.
After lunch we headed north up to see the 2 castles on the west coast. Cromwell's Castle & King Charles Castle.