It was done in the GIMP and took about an hour.
The hardest thing about joining the photos is getting the colour right. The light around Shandon (the steeple in the middle) was very blue, while the light to the right, around the North Chapel, was very red from the houses and street lights. Obviously you can’t see this in the monochrome version here, and that’s one reason I made it that way!
Matching the photos in detail was difficult too, as the tripod, no matter how careful one is, is never level (and it was too cold for me to be messing with the water level on the thing!)
I constructed the image from the left, and as I matched up photos the images had more and more white space underneath them. A quick crop at the end fixed that, and also let me concentrate on matching a slightly smaller area than I thought I’d have to. The two metal chimney stacks below Shandon didn’t match up without messing up the picture above it, crop the bottom out and it matched fine! 🙂