Visiting St. Peter's is an overwhelming experience and I'm guessing that the architects had that in mind when they planned this massive place. The dome that appears in this photo was designed by Michelangelo, but sadly he died before its completion. The structure with the darker, bronze pillars rising from the left corner of the photo is called the baldacchino, and was designed by Bernini. It is close to 10 stories tall (98 ft.). That, alone, give you a sense of the scale of the dome.
On the technical side, this camera and lens combination was the first time I was truly amazed by the capabilities of the Canon 5D. I shot with a high ISO and low shutter speed to get this shot and I was impressed by how little digital noise that showed up in the photo and how sharp the photo is - in spite of shooting without a tripod at 1/40 of a second.
Canon 5D Canon f/4.0 1/40 Canon 17-24mm 4.0L (17mm) ISO 1000