Long tunnels, high arches. This reminded me of "Lord Of The Rings" and the huge underground complex of the dwarves called Moria and consisting of vast chambers halls and mines.
In this Building the so called Bara Imambara you can find the entrance to a kilometer long underground tunnel to the Gomti river. It is believed that there are even longer tunnels to Faizabad and even Delhi (500km!!!). I heard of a whole unit of british soldiers who dissapeared in the tunnels and never made it out of there. These days the entrances are sealed, kind of at least :-)