Sandwick is the departure point for the passenger ferry to the tiny isle of Mousa, where you can see Mousa Broch, a fortified Iron Age stone tower rising about 40 feet high. The massive walls give a real sense of security, which must have been reassuring for islanders subject to attacks from ship-borne raiders. Exploring this beautifully preserved, curved-stone structure, standing on what feels like an untouched island, makes you feel as if you're back in 100 BC. From April to September, the ferry (£16 round-trip) departs for the island one or twice each afternoon. From May to July there are dusk boat trips (£20 round-trip) to catch the tiny storm petrels as they return from their day feeding at sea to their nests in the walls of the broch. The sight of them swarming in the half-light is something you'll never forget.