There are 20 mountains surrounding the four sides of Mahameru. One among them is the Trikuta. As per Puranas the city of Lanka - Ravan's abode - was built on the peak of Trikuta. Mahameru is on the Northern end of the Himalayas whereas Lanka is on the Southern side of Bharat (India). How did this happen? There is a story in Uttar Ramayana which illustrates the reason.
Once a small rift happened between Vayu Deva and Vasuki. They decided to find out who among them is the strongest. Vasuki entangled the Mahameru so that even Vayu was not able to enter the mountain. Vayu got very angry and appeared in the form of a cyclone which started to lash the whole world.
Even Mahameru started to tremble. The Devas became scared and they approached Brahma and Shiva. Together they approached Vishnu. Vishnu called both Vayu and Vasuki and ordered them to stop the fight. As a result, Vasuki straightened out one of the tangles which covered the Trikuta. Immediately, Vayu entered there and threw that part into the Southern Sea, towards the south of India. Viswakarma built a city on the peak of this mountain called Lanka.
Trikuta Mountain and Story of the origin of City of Lanka