Bangla Sahib Gurdwara
The most prominent Sikh house of worship in Delhi
Word to the wise: Dress conservatively and make sure to cover your head with a scarf before entering. You can buy them outside the gurdwara if you forgot to pack your own cover-up.
If you don't have the time to visit the magical Golden Temple in Amritsar, then the next best thing is the Bangla Sahib Gurdwara in Delhi. Built by Sikh General Sardar Bhagel Singh in 1783, it is a welcoming place of worship identifiable by its large flag-pole and golden dome. Take your shoes off at the entrance and take a tour around the temple. The sacred chants add to the atmosphere here and remember to try some prasad (holy sweets) handed out by the priest as you leave.
You can visit any day of the week, but it is advisable to avoid Sundays due to the mind-boggling number of devotees who flock here to pray.