The tomb of Shah Rukn-i-Alam (grandson of Shaikh Bahauddin Zakaria), was built between 1320 and 1324 and remains an unmatched pre-Moghul masterpiece.
From whichever side the city is approached, the most prominent thing that can be seen from miles all around is a huge dome. This dome is the Shrine of Sheikh Rukn-ud-Din Abul Fath commonly known by the title Rukn-i-Alam (pillar of the world). The tomb is located on the southwest side of the Fort premises. This elegant building is an octagon, 51 feet 9 inches in diameter internally, with walls 41 feet 4 inches high and 13 feet 3 inches thick, supported at the angles by sloping towers. Over this is a smaller octagon 25 feet 8 inches, on the exterior side, and 26 feet 10 inches high, leaving a narrow passage all round the top of the lower storey for the Moazzan, or public caller to prayers. The whole is surmounted by hemispherical dome of 58 feet external diameter. The total height of the building, including a plinth of 3 feet, is 100 feet. As it stands on the high ground, the total height above the road level is 150 feet.
Besides its religious importance, the mausoleum is also of considerable archaeological value as its dome is reputed to be the second largest in the world after 'Gol Gumbad' of Bijapur (India), which is the largest. The mausoleum is built entirely of red brick, bounded with beams of Shisham wood, which have now turned black after so many centuries. The whole of the exterior is elaborately ornamented with glazed tile panels, stringcourses and battlements. Colors used are dark blue, azure, and white, contrasted with the deep red of the finely polished bricks. The tomb was said to have been built by Ghias-ud-Din Tughlak for himself, but was given up by his son Muhammad Tughlak in favor of Rukn-i-Alam, when he passed away from this world during 1330 AD. -Wikipedia