The document discusses the early history of Lithuania and the use of a secret defense strategy called Kūlgrinda. Kūlgrindas were hidden underwater roads across swamps that were constructed by the ancient Lithuanians and provided safe passage between defensive structures. Undetectable from the surface, these roads were only known to locals and helped in defending against invaders like the Teutonic Knights. Remnants of Kūlgrindas still exist today, and some organizations offer excursions for people to experience traveling along the old secret paths through forests and swamps.