A small country that regularly gets loads of British visitors, particularly skiers, these days (I’ve been there myself), but so far I can’t find any evidence we’ve ever invaded with troops. During the Second World War, some British airmen did use Andorra as a route to escape from occupied France, but that’s maybe the closest we’ve come to sending British troops into Andorra. If anyone knows differently, let me know. Small countries make for small targets and have a disproportionately high representation in the short list of places we’ve never really invaded.