The National Mosque (Masjid Negara) is located in downtown Kuala Lumpur. The Mosque was opened in 1965 and can accommodate 15,000 worshippers. Islam is the official religion of Malaysia.
Even when you can’t enter the Mosque itself the surrounding grounds provide nice views.
Tourists can view the interior of the Mosque from 9AM to Noon (every day but Friday) and from 3 PM to 4 PM and 5:30 to 6:30 PM everyday. Those hours are not exact, it will close to entry earlier and can be closed for events. The time restrictions are for non-Muslim tourists.