Shore Crabs are a common sight in rock pools, under seaweed and in plastic buckets anywhere along the sude of Weymouth Harbour in the holiday season. If you try snorkelling though you have the chance to see the larger adult crabs which look quite different.
If you don't want to get wet you can always stick a cheap waterproof camera in a rock pool and bait it with some bits of raw bacon, as my friend Jess Evans did in her video below.