The Temple of the Emerald Buddha (Wat Phra Kaew) in Bangkok is a must see. It really is spectacular.
Be careful if you walk there as seemingly friendly people will come up to you and tell you it is closed for some reason and offer to call over a tuk-tuk (a three wheeled taxi) so you can see other temples instead.
Trouble is that you will eventually be taken to a tailors of some other kind of tourist store and the tuk-tuk driver will flip out and get abusive if you don’t buy anything.
So if you get approached near the Temple of the Emerald Buddha just ignore the touts and keep walking. If you engage in conversation you will find it very hard to shake them off.
Trust me, they aren’t your friends.