Sabz Burj is a 16th-century domed tomb near Nizamuddin, close to Humayun's Tomb and the dargah of Hazrat Nizamuddin Auliya. Despite the name, which means "green dome", the restored dome is blue, with tile work that shows Central Asian influence.
It is a small monument, but an easy and worthwhile stop while walking between Nizamuddin's larger historic sites. Look up at the dome and tile patterns, which are the main reason to pause here.