A line of concrete bunkers from the 1930s runs through the forested hillside above Bratislava's western suburbs, built as part of Czechoslovakia's pre-war fortification line. The bunkers were constructed between 1936 and 1938 to resist a German invasion — machine gun positions, artillery emplacements, and command posts carved into the hillside. The Munich Agreement made them obsolete before they were ever used.
The bunkers are now partially open for exploration. A number of them have been restored by the Slovak Fortification Research Group and can be visited with a guide. The largest is Henryk Bunker near Devínska Nová Ves, which has been restored to its 1938 condition with original equipment and fittings. Tours run on summer weekends; check the group's website for dates.
The sites are accessible by bike from central Bratislava — the ride takes about 45 minutes along the Danube cycle path toward Devín, then uphill through the woods. The bunkers combine well with a visit to Devín Castle.