Lying in peninsular Malaysia's northwest Kedah Province, Bukit Kaya Hitam is an uninteresting border town opposite Thailand's Sadao. People generally go straight through Bukit Kaya Hitam in either direction, although there is some decent duty-free shopping.
Bukit Kayu Hitam is known as Black Forest by its English transliteration and basically consists of a shopping center and a golf course in no man's land - the patch of land in between Thailand and Malaysia. At the shopping center you can pick up cheap booze and cigarettes, along with a decent range of electronics and perfumes.
Long distance buses between Thailand and Malaysia invariably use this checkpoint, while Bukit Kayu Hitam is the starting point of Expressway E1, the north-south expressway that runs to Johor Bahru and Kuala Lumpur.
The best way to Bukit Kayu Hitam is by bus, from either Malaysia or Thailand - trains cross at the nearby border point of Pedang Basar. Whichever direction you are headed, be sure to book a bus beforehand as buses generally do not pickup at Bukit Kayu Hitam. There is a bus south to Kuala Lumpur; however, the nearest international airport is at Hat Yai in Thailand, a 40-minute drive away.