Topped with a 160ft minaret, this pale limestone structure is the national mosque for American Muslims. It is delicately inscribed with Quranic verse, so it appears to float above Massachusetts Ave. Inside, the mosque glows with bright floral tiling, thick Persian rugs and gilt-trimmed ceilings detailed with more Quranic verse. You can enter to look around; remove your shoes, and women must bring scarves to cover their hair.