Columbo take the direct bus to Kataragama that leaves every
hour from Columbo's main bus terminal. Last time I was there it
cost about 500 rupees (about $6 US) one way and took anywhere from
6 to 9 hours depending on what time of day you left.
Place is conveniently located 4km from Kataragama town next to
Jayasumanaramaya Buddhist monastery.