Bornholm

Most days start in a car park above the rock. Kit goes in the boot, you drive to whichever coast is in the lee, walk down over granite and swim out; the surface swim is part of the deal, and pairs often make two entries at different points around the island rather than repeat one. Boat days exist for the offshore wrecks and the run out to the Ertholmene islets, but they are the exception, and the island is small enough that a blown-out north coast means half an hour in the car to the east or west side instead.

The granite is old basement rock, and where it goes under it keeps its shape: slabs run on into vertical faces, cracks and boulder gullies with pale sand in the gaps. It is not spread evenly. The north and north-west, around Hammeren and Vang, hold the steepest rock, the east coast has lower reef, and the southern end of the island runs to sand. What grows on it is Baltic rather than North Sea, with wrack and mussel banding the shallows at roughly a fifth of ocean salinity in place of the sponge and anemone cover found further west.

There is no closed month, so the question is what you want from the water. June through September brings the warmest water, the longest light and the steadiest days for boat work, with April, May and October cooler but still workable. Late winter is dim and cold on the surface and the clearest of the year below it, which is when the shore sites look their sharpest, and in hard winters sheltered bays freeze enough for ice diving with proper cover and training. The mix suits pairs and clubs running their own days more than divers wanting a guide for every dive.