This is Bibi-ka-Maqbara, the "poor man's Taj",
the tomb of Rabia-ud-Dauani, the wife of Aurangzeb,
the son of Shah Jahan, the guy who built the
Taj Mahal. This tomb, which we did not visit,
is said to be a poor imitation of the real Taj,
using plaster instead of marble. I understand
that Aurangzeb is buried elsewhere under a
large mound of dirt.