Pretty, accessible Yeh Pulu is barely 10 minutes from Ubud and a good side trip from the more popular Goa Gajah. It's only a small complex accessed by a long and delightful walk through the rice paddies on the outskirts of Ubud.
Yeh Pulu sits between the Petanu and Pekerisan rivers and literally means 'water of the stone vessel' in old Balinese. The 25m set of relief walls from the 14th century depicts Hindu gods as well as ordinary people going about their lives.
Very few people visit this site, so you won't need to fight the hordes or wake up super early to visit. The best light is from 3 pm, and by 5 pm, the sun will be setting, and you can get some gorgeous photos.
Your driver from Ubud will know where to take you, but if you go by scooter and drive yourself, follow google maps and head for the southern entrance. The entry price is R30,000 (about US$1.80) or R20,000 for locals. There is a small warung along the path, and I'm sure they'd love your patronage for a simple nasi campur. However, on the road back to Ubud past Goa Gajah, there are many restaurants, including some very good ones that serve the local delicacy Bebek Goreng (fried duck). Bebek Joni is particularly good and has a beautiful rice paddy view. On the other side of the main road, Kelapa Muda is charming and great for kids to wander around, while Sawah Indah has a fantastic spot overlooking the jungle and river.