Bedugul is located about 50 km north of Denpasar on a main route from South Bali to North Bali.
The area is served by regular bemos which depart from Batubulan terminal in Denpasar in the south, and from Singaraja in the north. The Perama bus company (http://peramatour.com) has no local office in Bedugul so if you planning go further from Bedugul, buy ticket in Kuta, Ubud or elsewhere.
A common way for visitors to appreciate this beautiful mountain region is to hire a car and driver for the day from their base in South Bali. Make sure you have a driver who knows the area well ask questions to determine this, and fix the price for the day in advance. Depending on the class of car, expect to pay between Rp 500,000 and 600,000 including petrol. Car parking fees and any entrance charges will be extra, and it is always appreciated if you offer to buy the driver lunch.
Another option is to hire your own car and drive up here. Be sure to bring a good map though, and when in doubt, always ask locals for directions.