If you've never been, you should visit the Emerald Buddha temple and the royal palace and the national museum nearby. But personally, I like more Wat Saket (the temple of the golden mountain) and the view from the mountain itself Also very cool Wat Arun, especially its amazing pagoda, worth a visit. Basically there are many more temples, some you can visit on the way, for example if you get to Asiatique. Which I highly recommend. Firstly, one way from or to BTS Saphan Taksin station you can take a free river boat from Asiatique, or a longtail or a pleasure boat, I strongly recommend to do it at sunset, the view on Chaopraya is gorgeous. Secondly, there are some nice temples on the way if you walk from the station to Asiatique. Finally, in Asiatique you can eat at an atmospheric seafood restaurant, buy some swag, eat some cool ice cream, walk along an excellent promenade, even ride the Ferris wheel. Of course out of the parks I advise you Lumpini, as it is in the center, you can walk somewhere along the road. In the evening you can visit Kaosan Road, a shopping street - a perpetual find-market. If you want an observation deck, first of all you can visit Bayok Sky - the 83rd floor has a good view It's best to go not very early, but in the morning while there are no crowds. Secondly, the skywalk is a glass-floored observation deck at King Power Mahanakhon. The Jim Thompson House Museum is also worth a visit - architecturally beautiful and the exhibit is interesting. The Erawan Museum is interesting - a giant three-headed elephant and cool, but a bit far from the center. You can visit Sea Life Bangkok - the aquarium, I really like it. Bangkokers asked to add Benjakiti Park to my list, which is connected to Lumpini by a bridge In the Lumpini Park area, it's good to go to a rooftop bar at night/evening. If you like parks, Suan Luang Rama IX has 80 hectares of themed areas in Chinese, Japanese and European styles. A third favorite park is Chatuchak, it has two other small neighboring parks that are also great to walk around. And Chatuchak as a market is also interesting, it seems to be the biggest in SEA.
Erawan Temple is memorable, but how interesting it will be for you I don't know. So the standard set of the Royal Palace, WatArun, Iconsiam, KhaoSan and Chinatown in the evening. There are more exotic places like museums, lots of temples of different orientations, walks on Chao Phraya in the evening, etc.
Also very cool Wat Arun, especially its amazing pagoda, worth a visit. Basically there are many more temples, some you can visit on the way, for example if you get to Asiatique. Which I highly recommend. Firstly, one way from or to BTS Saphan Taksin station you can take a free river boat from Asiatique, or a longtail or a pleasure boat, I strongly recommend to do it at sunset, the view on Chaopraya is gorgeous. Secondly, there are some nice temples on the way if you walk from the station to Asiatique. Finally, in Asiatique you can eat at an atmospheric seafood restaurant, buy some swag, eat some cool ice cream, walk along an excellent promenade, even ride the Ferris wheel. Of course out of the parks I advise you Lumpini, as it is in the center, you can walk somewhere along the road. In the evening you can visit Kaosan Road, a shopping street - a perpetual find-market. If you want an observation deck, first of all you can visit Bayok Sky - the 83rd floor has a good view