Established in 1965 as a symbol of the newly, independent Malaysia, the National Mosque of Malaysia (also called Masjid Negara) is definitely worth checking out.
The best way to get to that area, is taking the Kelana Jaya line (the pink one on the map) of the Rapid KL to Pasar Seni. That would drop you off at the old KL Railway Station. Then you will have to follow a series of bridges and go through a tunnel to get to the mosque. If coming from the National Museum, you could walk to it from there, but it can get very confusing. You are better off going back to KL Sentral, and taking the train from there, as getting there by walking is very confusing and time-consuming. I learned that the hard way.
Entering the mosque can be tricky, as it is only open to non-Muslims at certain times. If you can get there early enough, check the times, and if not open at the time, you can visit some of the other attractions nearby in the meantime, like the Islamic Arts Museum.
Or take the time to walk around the exterior, which is enough reason to come in the first place. Built in the modern style instead of the traditional Islamic style, with its long tower and the pointy, blue umbrella-like dome, it is very nice to look at.
When entering, you will have to take off your shoes, and the dress code is very conservative. But a purple robe is provided for those who need to cover up at the entrance. And it is free to enter.
Some things to check out once you enter, include the mausoleum, where the tombs of past Malaysian leaders are located. Unfortunately, there were no English descriptions about it, so I had to look it up myself later on. That is located under a blue umbrella roof. Also, there is the main prayer room, but only Muslims are allowed to enter. But you can still look inside from the doorway, and feel the breeze from the air conditioner inside. Other than those two things, there is not much else to see, other than admiring the architecture of the place.
So I would say, the inside is very nice to look at, but not quite worth it enough to really go out of your way to see it, and/or wait until the time when non-Muslims can enter. If you don't have the time to enter, definitely take the time to see the outside, which is just as nice and worth it. And walking around the outside is allowed at any time. ;)
This review is the subjective opinion of a TravelPod member and not of TravelPod.com.