Achankovil in Kerala is both the name of a river and a village, famous for the Shastha Temple. This village is located deep in the forest, accessible only through the forest routes. You can reach Achankoivil from both Kerala and Tamilnadu side. The road from Tamilnad side is better motorable.
See also How to reach Achan Koivil and Punalur to Achankoil. Buses (KSRTC) from Kerala to Achankovil operate both from Punalur and via Sengottai. During the Sabarimala pilgrimage season, the route get a a bit busy.