First, the obvious World Heritage choices
- Lal Quila - The Red Fort
Some of the images on the site http://www.econ.ucdavis.edu/faculty/fzfeens/India_trip_and_photos.html
An idea about the light pollution around the Red Fort area can be obtained from this image here at http://www.hat.net/album/asia/india/05_cities_and_maharajas/03_old_delhi/detail032.htm
- Humayun's Tomb
- Qutub Minar and the Alai Darwaza
On this website 
http://www.aulia-e-hind.com/dargah/delhi.htm
- Astronomical observatory of Jantar Mantar - a masonary positional astronomical observatory built around 1724 by Sawai Jai Singh
- The Pir Ghaib Observatory built by Feroz Shah Tughlaq, in the 14th Century. In late 19th century, the monument was used again for astronomical purposes, as an observing tower of the Great Trigonometrical Survey.
- Gandhiji's Samadhi at Rajghat
- Fatehpuri Masjid
- The very modern day monument - the Akshardham Temple
Image on the website http://tourism-delhi.info/Akshardham.html
