This tunnel was neccessary to provide direct connection between Krisztinaváros district of Buda and the chained bridge (Lánchíd) so that you wouldn't have to climb the castle if you want to get to Pest. It was planned by Adam Clark based on the ideas of Daniel Novak, the final plan was accepted in 1845. Constuction was delayed by the revolution in 1848, finally it was opened to the public in 1857. The tunnel is 9.5 metres wide and 349m metres long, a toll had to be payed till 1918 when it became free to cross the tunnel. The western facade facing Krisztinaváros was destoyed in WWII, the current one was built in 1949. The last modernization of the tunnel took place in 1973, new blowholes were installed.