As one might expect from the former capital of the British India, Calcutta has plenty of beautiful buildings (administrative, mansions etc), mostly built in the Victorian style. Some of them are preserved and still in use, while many are in decay.
One interesting destination is the Indian museum, established in the lat XIX century. Has art, archaeology, geology, zoology/botanics as well as mineralogy exhibits. Very old school inside and outside.
The most recognizable landmark is the Victoria Memorial, opened in the early XX century. Features art and history exhibits and a nice park with artificial lakes.
Barbwire on top of the Victoria Memorial fence. Needed to keep the barbarians outside..