Last week, I learnt the word "tripoint", which is the place where three countries or counties meet.
It first cropped up on University Challenge: a starter for ten was to identify the city at the tripoint of France, Germany and Switzerland. The answer was Basel.
Having been slightly obsessed with Cairo, Illinois, since going to the Cartwright and Jordan Cornerhouse exhibition on Thursday, I've been looking at various maps and information on the town, and discovered that it too is located at a tripoint: where Illinois, Missouri and Kentucky come together.
It got me thinking about other tripoints, and I remembered visiting Alfred's Tower some years ago. I like follies and this one sits on the border of Somerset and Wiltshire on the Stourhead estate, with a panorama that takes in the tripoint of Somerset, Wiltshire and Dorset. Check out the aerial photos on the official King Alfred's Tower website: not only is the tower located at a tripoint, it is also triangular in plan.