Kūlgrinda
Kūlgrinda (plural kūlgrindos; from the Samogitian kūlis 'stone' and grinda 'pavement', itself from grįsti 'to rake, pull together') is a hidden, usually winding, underwater stony road or ford across swamps, swampy areas, lakes, or along rivers, used as a defense in the lands of Baltic tribes, in particular, in the history of Lithuania. Similar secret roads made primarily of wood and ground were known as medgrinda (from medis, 'tree') and žemgrinda (from žemė, 'earth, ground') respectively.