So I went searching.
For the blue dome thing. And really, that's what it is. Nila Gumbad means blue dome. A conveniently easy name to remember.
The tomb sits near the railroad tracks and is surrounded by a wasteland of railroad ties and other trash.
Humayan's tomb and all it's well-kept glory is just right there nearby. But the blue dome thing is outside it all.
Maybe something will be done about it. Yet, history, it seems, doesn't care to preserve every story, even when we build giant tombs to remember them.