Lal Gumbad is the red-sandstone tomb of Shaikh Kabir-ud-Din Auliya, built in the late 14th century during the Tughlaq period. Its name means "red dome", and the monument is one of Delhi's early surviving tomb structures.
It is a quiet historic stop rather than a major headline sight, best paired with other south Delhi monuments if you are exploring beyond the usual Mughal landmarks.