This is an extraordinary, out-of-the-way private museum. There is easy access from the BTS Sky Train, just a 15 minute walk.
The Erawan Museum is known for its giant three-headed elephant art sculpture as exterior. This is the first and biggest hand-carved sculpture in the world--43 meters high.
The garden surrounding the statue is a pleasant mixture of kitsch and calm, whereas the interior is over-the-top rococo!
The museum in the basement is only so-so, but the shrine room under the elephant's back is superb. It is a great place to meditate, as it is a used as a place of worship by Thai Buddhists. There are a number of rare old statues from different eras.
I live in Thailand so I did not have to pay the exorbitant Foreigner admission fee of 400 Baht, but 'only' 250 Baht. Still quite a bit more than the 40 baht that locals pay. The discount is not posted, so you have to ask at the ticket window and you must show proof that you live in Thailand. I used my Retirement Visa, and my friend showed his Thai driver's license.
All in all, a pleasant way to spend an afternoon.