Ayutthaya Historical Park is worth a visit while in Thailand. One of the more interesting and photographed sights on the grounds is the Buddha Head in a Tree. This stone buddha head was decapitated from its base during a 1767 Burmese attack and somehow ended up over time embedding itself into this tree’s tangled roots. Even its shade matches the bark making it appear as if it were a natural part of the tree.
(Ayutthaya Historical Park Tip: If you’re going to see the temples of Siem Reap on your trip, you may want to skip these ruins or see Ayutthaya first since you will probably be a bit underwhelmed in comparison to what Siem Reap has to offer.)