We’ve many times threaded through the shifting gravel banks to enter the River Ore in Suffolk without seeing what is sometimes hidden behind – a clean, warm, tide-free swimming pool, 10 feet deep in the middle and perfect for a dip on a hot afternoon in August. Local residents told us it appears every few years but is it’s an easily-guarded secret – you can’t even see it from the top of the beach by the coastguard cottages. Not sensible to try to get to it by boat, of course.