The problem of the dome
A hemispherical dome pushes outward at its base. The usual answers are buttressing, thickening, or chaining. The builders at Bijapur used a different one: eight intersecting arches inside the cube, forming a ring that carries the dome’s thrust inward onto itself.
The result is a single unobstructed chamber roughly fifty metres square under a dome of comparable span — one of the largest unsupported interior volumes anywhere before the modern period.
The whispering gallery
The gallery running inside the dome’s base carries sound around its circumference with unusual clarity. It is a by-product of the geometry rather than a designed feature, and it is now the reason most visitors come.