Directions to the ring:
As you are exiting the building and go through the iron gates (not the ones all the way out at the attraction entrance, but the ones right outside the building and just before the carriage) look down. The ring is embedded in the ground directly in line with the center of the main gate if it were closed. The ring is small, about half the diameter of what you would expect. At first glance it just looks like a retaining hole in the pavement that you would drop a gate lock into, but if you get down and look at it you'll see that there is actually the outline of both the band itself and a jewel. If it is not broad daylight out, you will have a difficult time seeing it.
Details on the proposal:
We had already been in the park for several hours with me playing tour gide. By the time we got to the Haunted Mansion she was totally used to me stopping and pointing out little details. The entire day I had the ring in my pocket where I wouldn't have to fumble and search for it when the moment came. As we exited the ride I took her over and showed her the mural listing all the brides, and then as we were about to go through the gate I said, "oh, and hey... check this out.."
I got down on one knee so I could point out the ring, and she thought it was pretty cool. "And speaking of rings..." I said, and then presented her with the real thing. A crowd of people just exiting the ride stopped dead in their tracks to watch, as she burst into tears (that's a good thing). She said yes, I got up and gave her a big hug and a kiss, and then she had to go sit down for a few minutes. She kinda had that dopey love-struck grin on her face, and she couldn't stop fiddling with the ring. She was completely blindsided, she had no idea that I was going to propose to her that day. She figured it was coming at some point, but she never expected it right then and there.
When I mentioned to her later that several of my co-workers were moritified that I planned to propose to her in front of the Haunted Mansion, she simply replied, "They don't know me very well, do they?"