The construction effort reflected the tunnels’ importance to the German military during the Second World War; they were built to defend against a potential Soviet invasion across the critical region between the Oder and Warta rivers. While the tunnel network often steals the spotlight, the Ostwall Fortifications also featured an array of aboveground defenses. In addition to serving as a winter refuge for bats, the Ostwall Fortifications have become a popular destination for history buffs and curious visitors.