I've uploaded a few pictures. The one I thought was the pavilion used by the officers as a swimming pool is in fact a mosque (Moti Masjid)- a big mosque made of white marble built by the Mughal emperor Aurangzeb at the Red Fort complex from 1659-1660. I've put in a picture of the Jama Masjid mosque, which survived and is next to the Red Fort. It's a huge space and after the madness of Chanda Chowk is a surprisingly peaceful oasis in the city. The Lahore gates are the main entrance (where Jennings and his daughter were killed). When we visited the fort there were armed soldiers and metal detectors at the gate. With the possible hanging of a bomber pending the government were half expecting some kind of attacks on national buildings. I got confused reading the book - where Dalrymple talks about the maze of streets that greet you as you first come inside the fort - how it's a mini town inside the main city. Reading on I discovered that most of those buildings and much of the palace were demolished by the British. Now, when when you walk in through the Lahore Gate, you come into a lengthy arcade of stalls (selling souvenirs and tourist tat) which presumably are the ones referred to as being used by the British officers after the occupation (and some of the souvenirs are probably the same).
Moti Masjid
Lahore Gate
Barracks

The eyesore that is the British Barracks was built in the 1860.