Grassholm might be tiny but it has thousands of noisy stinky gannets on it: about 10% of the world’s population (I can vouch for its impressiveness myself). Consequently you can’t set foot on it, but it would seem intrepid solitude-seeking prehistoric people did, as Iron Age pottery has been found there. Presumeably under a pile of gannet poo. Perhaps the gannets hadn’t taken up residence at the time. Or perhaps they had (what’s for tea, mum? Omlette with gannet and fish. What, not Again??)The island is miles away from any others and about 10 from the mainland.