This is the beautiful main mosque in Old Delhi, built of the same red sandstone as other sites around town, like the Red Fort. After the crowds and noise of the streets outside, it was quite nice to climb the steps and enter the large courtyard. It also gives a good birds-eye view of the crowded streets outside.
After a few years of living in the Middle East and visiting various mosques that are open to non-Muslims, I know to come prepared in my long sleeves, long pants and headscarf. Nevertheless, a man leapt out after I had taken off my shoes and started to enter the gate, and told me I had to put on an extra covering. I came to refer to it as "my cartoon abaya". (It's not a scam as far as I could tell, they just seem to make any Western woman wear the cartoon abaya, no extra charge.)
The Indian locals who were inside the mosque LOVED this get-up and I spent lots of time posing for photos with many polite ladies, little kids and one massive family.