Explore the ruins
The Phra Prang Sam Yot temple will take you a day to absorb. It's in the Bayon style of Khmer architecture, like the more famous Angkor Wat, and is characterized by distinctive Khmer elements such as bas-relief and blind doors or windows.
When it comes to interacting with the monkeys, there are a few things to keep in mind:
Don't look them directly in the eyes, as they perceive this as a challenge or threat (and can attack). Don't smuggle food in your purse or pants (they will know). Overall, be kind and stay relaxed. Animals are sensitive to energy, and while a stick for self-defense comes with the 20-baht entrance fee, try not to use it. They might steal your stuff, but don't forget that you're a guest at their dinner party.
Watch Baraka
It'll get you in the mood for your trip and prepare you for some of the things you'll encounter.