A little gem
Far up in the north east of Cambodia, in Ratanakiri province is a little town called Banglung. It is surrounded by forests which boast a number of beautiful waterfalls, a volcanic crater lake called Boeng Yaek Lom (which is perfect for swimming in after a long dusty day on bikes), strange burial grounds and little gem mines where men climb 15 metres down holes 2 feet wide scouring through the dirt for zircons.
Either fly direct to Banlung from Phnom Penh (in an old Chinese Antonov prop-plane) or make your way to Stung Treng and take a pickup-taxi from there.
We loved all of Cambodia during our month there and were suitably impressed with the temples around Angkor, but our time spent in Banlung was the unexpected highlight of the trip. Highly recommended.