Riezupe Sand Caves form a long man-made labyrinth north of Kuldiga, dug for the clean white quartz sand once used in glass production. Only part of the two-kilometre tunnel system is open to visitors, but even the short guided route gives a strange, close-up sense of the place.
Expect narrow passages, cool air and a bit of crouching in places. It is an easy add-on to Kuldiga's old town and Venta Rapid if you have a car or can arrange a taxi.