So, we visited St Michael's Mount yesterday, and very enjoyable it was too. And we discovered the most fun you can have there:

1. Wait for the tide to come in
2. At the point the causeway starts to get covered in water, get a good vantage point on the hill
3. With binoculars or a decent telephoto lens, enjoy the sufferings of the those who tried to beat the tide:

The boat across, incidentally, is a grand total of £1.50, and a great ride.