The document discusses Eagles' Nests, a system of 25 castles and watchtowers along the old Polish border with the Kingdom of Czech. It describes the Eagles' Nests Trail, a 163km tourist trail between Krakow and Czestochowa passing through the castles. The trail was established in 1948 to showcase the most attractive areas of the Krakow-Czestochowa Upland. In the Middle Ages, Polish king Casimir III the Great created this fortified system to guard the borders and trade routes.