The Taj Mahal is by far the most beautiful man-made structure I have ever seen. Alone, it is almost worth making the trip to India. Pictures do not do it justice, and words even less. See it.
The site is crowded. Plus hawkers galore. It's run by the Archeological Survey of India (A.S.I.). I've noticed that A.S.I. sites in particular seem poorly run, and the hawkers here have taken up the slack. In contrast to the City Palace in Jaipur or Mehrengarh in Jodhpur, where there are fewer hawkers. A.S.I. sites have little in the way of museum shops or facilities, and they do things like make you park far away so rickshaws can make a buck getting you closer.
The Taj follows other memorials. Large garden. Raised plaza. Memorial in building atop plaza. The difference with the Taj is the working of the building itself. Exquisite marble inlay work. Outside are black marble inlays of Q'uran verses. Inside it's flowers and other types of unlay. Marble railings with ornate latticework carved from single pieces of marble. If you make a mistake you start over with a new piece of marble. The building is symmetrical. A mosque faces west on one side of the Taj. A similar building faces east, though it is not used as a mosque for it's east-facing ways.
Shah Jahan built it in memory of his wife Mumtaz. He apparently intended to build a black marble version for himself across the Yamuna river with a marble bridge connecting the two. Across the river you can see the beginnings of work on his own memorial, though it's just brick walls. Shah Jahan was deposed by his son, who did not want to spend money on the second Taj. He imprisoned Shah Jahan in Agra Fort, within sight of the Taj. Obviously, the second Taj was never built.