The Angurukaaramulla Temple is a very cool place to visit if you're in Negombo. It's best known for its epic statue of the Buddha, and its dragon-entrance - inside you find detailed murals that date back centuries. There is also a 300+ year old ruin of a historic library here, covered in moss.
The Buddha statue out front is six meters tall. You walk through the dragon's mouth to enter the temple - the dragon is supposed to ward off evil spirits. The premises are a wide-open space with plenty of trees by the edge and a pond in the middle (with turtles in it).
Inside the temple are amazing murals, sculptures and paintings on the ceiling, depicting the Buddha's journey to enlightenment and stories of Sri Lanka's former rulers from the Mahavamsa.