Wat Phra Kaew is in the area of the Palace, you can visit all at once. Very pretty building and the surrounding gardens make the place chilled and natural.
The red hall in this temple is outstanding, like nothing I've seen in Ko Samui. Very nice place, there are many possibilities of taking great pictures.
The bridge is nicely lit at night and it's kinda romantic to stroll down. There are many cafes at the banks where always many people sit. There's also a little park with benches. The river view from the bridge is beautiful too.