Hidden beneath partly-wooded hills 1.7km southwest of Hotton, the Grottes de Hotton are some of Belgium’s most awesome caves. Sculpted grottoes sprout pretty stalagmites and weird ‘eccentrics’ – mini corkscrews or horizontal protrusions apparently defying geological logic. However, the real highlight is descending a former siphon through upturned vertical strata into a dramatically narrow, 37m-high subterranean chasm.
Visits are only by relatively long guided tours (English often available) involving 580 steps. Tours start roughly hourly in summer, dropping to around five daily departures in shoulder season and only three (at 12.30pm, 2pm and 3.30pm) on Saturday and Sunday in winter. It's always worth calling ahead to check the day's departure times. Dress appropriately for spending between an hour and 90 minutes at 12°C. Access without your own vehicle is difficult.