Wat Arun
Traffic in Bangkok, like pretty much every other major Asian city, is horrendous. Taking the SkyTrain/MRT mass transit options can be pretty quick and convenient. Sometimes though, an express boat is what you really need, and they're cheap too! On the way to the Grand Palace, we paid at the manned ticket booth and received our tickets as well as apparently complimentary juice boxes. Not sure if the juice boxes are a regular thing or just some random promotion. On the way back however, it seemed that the system relied on manual fare collection, which is, let's just say, never perfect.
On the west bank of the Chao Phraya River, somewhat opposite of the Grand Palace, is the Temple of Dawn. Also known as Wat Arun or by a super long Thai name with lots of repeating letters I have no hope of pronouncing correctly. The central tower is known as a prang in Khmer architecture, and stands over 200 feet tall. The level of ornate detail and decoration that has gone into not only Wat Arun but the other significant temples in the area is superbly impressive.