You can go here by MRT. You can stop at Brash Basah or Dhoby Ghaut Station. It's not too far.
National Museum of Singapore is a place to get to know the history of Singapore. This museum located on 93 Stamford Rd, Singapore 178897. It opens everyday from 10am to 7pm (The last admission is around 6 or 6.30pm). I bought the ticket from Klook, the price is around SGD15. You can also check their site or other travel site to book the ticket. Here, you can wonder around the museum to get to know about the History of Singapore in detail.
The Glass Rotunda Room is the best place to visit here. You'll experience the difference type of museum thing. Here you feel like you're in the nature. (You must visit it yourself to get the feeling. I can't describe it well).
This place has a unique interior design. And you can buy the souvenir too if you want.