The idea of a tunnel under Castle Hill emerged at the time of the beginning of the construction of the Chain Bridge. The bridge facing Castle Hill together with the tunnel really united the town: Christina Town and the Buda Hills - which became more and more popular with people as a holiday resort and destination of trips - became directly accessible. Count István Széchenyi, who initiated the building of the bridge, had started to raise the necessary money already in the 1840s. The designer of Chain Bridge, William Tierney Clark made the plans but they did not start to build it because of the 1848 revolution.
A conservative politician, József Ürményi revived Széchenyi's plan after the opening of the bridge in November 1849. He set up the joint-stock company that organised the construction of the tunnel between 1853 and 1856. Adam Clark, the chief architect of the bridge - who settled down in Hungary - was responsible for making the final plans and carrying out the building. He used his former employer's plans as well.
The construction works started at the beginning of 1853. 200-300 workers had been drilling through the hill for 7 and a half months. 80,000 kgs of gunpowder was used to blow up the hard stone of the hill. The lime needed for the construction was gained from the hill itself, and the exploited stones were used for building the Buda quayside. The builders had a lot of trouble with the water continuously leaking from the holes of Castle Hill, as protection against ground water became the biggest technical problem of maintenance. The ceremonial opening was held on 30 April, 1857.
The Tunnel was relatively cheap - compared to the total cost of 6 and a half million forints of the building of the Chain Bridge. It cost only 524,000 forints. People had to pay for using the tunnel - and the bridge - until 1918. The total length of the barrel-vaulted tunnel is 340 meters. Its width is 9,5 meters, its height is 10 meters at the gates and 8 meters in the middle. The entrance at the Chain Bridge was built in neo-Classical style. The facade looking ontoChristina Town - which was completed only in 1869 - reflected the Romantic architecture of the age. It was destroyed in World War II, and it was rebuilt with plain stone blocks in modern style in 1949.