Meghnad Saha Planetarium & Science Centre

Hours: Check locally for show timings; typically 10am-5pm
Entry: Rs 20-50 per person (approximate; subject to change)
Shows: Dome shows at set times; check schedule on arrival
An unlikely but genuine delight. The planetarium was inaugurated in 1994 in an unusual public-private collaboration between the Japanese Optical Company Goto and the Indian and Japanese governments. The dome shows (typically in Bengali) are primarily aimed at school groups but are visually engaging regardless of language. The attached Science Centre has interactive exhibits that are well-maintained and genuinely educational.
This makes an excellent half-hour stop if you have children in tow, or if you want a brief air-conditioned respite from a hot afternoon.