Varkala Tunnel, also known Varkala Turuthu, is one of the historic sites of the region. This site was constructed by the British to establish an inland waterway that was meant to serve as a trade route. The construction of the long tunnel was started around the mid-1860s and took around 14 years to complete. With a length of around 924 feet, the tunnel played a vital role in transferring ferry goods and people from Thiruvananthapuram to Kollam during the pre-independence era. The tunnel is located under the main cliff of the region and represents the architectural excellence of the workers and engineers of that era. Built under the supervision of T. Mahadeva Rao, the dewan of Travancore, the tunnel also provides way to Varkala's TS canal, which passes through this delicate structure.