Ideas for unique experience?

This might not be unique enough or personal enough to qualify for what you want to achieve, but since you're going to London anyway, consider attending the Ceremony of the keys at the Tower of London. You didn't indicate when you're leaving, but you'll need to book your date well in advance. http://www.hrp.org.uk/TowerOfLondon/WhatsOn/theceremonyofthekeys

What are the two of you interested in? What is HE especailly interested in? I can think of lots of wonderful things to do in London that might or might not be great for you. Personally, I'd love to go to Kew Gardens and spend most of the day just walking around together enjoying the flowers and other plants. But my husband and I LOVE flowers! Others would find spending a day that way torture. You could also plan a day trip to a special locaiton. I can't speak to Paris or Bruges, but from London you can easily get to LOTS of great places. Windsor, Canterbury, Dover, York, Stratford-upon-Avon, Oxford, Cambridge (you could do a 'punting' trip down the river and a picnic), Winchester, Bath, Salisburry, Brighton (for a day at the beach)and many other places are easy to get to by train.
Or maybe a trip down the Thames on a 'jet boat', or a special picnic in one of the lovely parks (... a loaf of bread, a jug of wine and thou...), theatre tickets to a show HE would LOVE (Shakespeare, drama, comedy, a musical).....

Ok, I know you said no food, but I think of this experience as being about more than food. We went to the Dans Le Noir restaurant in Paris (there is also one in London). You eat completely (and I mean completely) in the dark! It was definitely the epitome of a "unique" experience. You may think you have been in the dark before, but until you experience this restaurant you will realize you haven't been. It's pretty incredible. Half of my party almost freaked out to the point where they had to leave. I just wanted to throw this idea into the mix in case it interests you at all. It was quite the story to tell once we arrived back home. Ps. Just for full disclosure, I know some major cities in the US have restaurants like this as well. We will just always connect it with Paris. Google Dans Le Noir Paris and you should find the website!

Toni - You brought up a very good question. He's interested in history, cars, and things that are off the beaten path. I thought about theater tickets, but he's not big on theater and I'm already dragging him to our local one several times this year. We are going in August, if that helps. Danelle - That's an interesting suggestion, I'll look at it, thanks! The reason I said no food is because, for some, having hugely expensive meals is a unique experience. However, for us, we don't like to spend a lot on food, we'd rather have a memory of an experience.

How about a Segway tour? They have several different ones in Paris (don't know about the other cities, but you can google it).

Behind the Scenes Tour of the Eiffel Tower, http://www.localparistours.com/behind-the-scenes-at-the-eiffel-tower-paris_14838 steam bath and massage at the Hammam at the Paris Mosque,
http://www.traveltowellness.com/parishammam hiking from Stonehenge to Salisbury http://englishcountrywalks.com/walks/9/default.html canal boat tour to Regent's Park via Jason's Canal Boat tour If a trial is in session visit the Old Bailey and watch the proceedings Tour the London Motor museum Apply to mudlark along the Thames Would he like to watch rugby or cricket or soccer?

Since he likes cars- what about a factory tour? I did a quick search and found that you can tour the factories for Aston Martins, Bently and Rolls Royce, Triumph motorcycles, Mini Coopers, Jaguars, Lotus custom sports cars, and others. Some are closer to London than others. Some are even free (some asked for a donation to a charity they sponsor) so your cost would just be getting there. Here are some sites I found
http://www.bentleymotors.com/world_of_bentley/bentley_factory_tour/ http://www.jaguar.com/gl/en/experience/visits/factory_visits http://www.morgan-motor.co.uk/mmc/factoryvisits.html http://www.bmweducation.co.uk/coFacts/linkDocs/PLANT_TOURS_V3.pdf http://lotusdrivingacademy.com/hethel/factory-tour

Vaux-le-Vicomte is a great suggestion and one of my absolute favorites... but it's only 30 min from Paris (not 2-3 hrs) then a 15 min taxi ride from the train station. It's listed in RS Paris guide with instructions on how to get there.

In Bruges we did a segway tour and saw much more than we had walking around the city. It was easy to learn, seemed safer than biking in the crowds, and we got to see the green spaces and canals. It was not expensive ( relatively speaking) and a great memory even today. I recommend the 2 hour experience. There were 4 of us and we were the only ones to book so it was like a private tour at the public rate.
Balooning is fun the first couple of times, but I'm not much on getting up so early.

If he has an interest in history, there's a chateau outside of Paris (2 or 3 hours by train; pleasant ride) that that might really interest him. On Saturday in summer and early fall, it is open at night with the chateau and gardens lit by candles, which is stunning. On Sundays, when I was there, the fountains were on. The gardens are well preserved, and the house is still furnished (unlike Versailles). It's lovely, uncrowded, quiet, and you really get a sense of history... of what it was like in the 17th C. The chateau is Vaux le Vicomte (http://www.vaux-le-vicomte.com/en/index.php). It was built by Nicolas Fouquet, finance minister to Louis XIV. Louis ultimately imprisoned Fouquet and used Vaux le Vicomte as the model for his redesign of Versailles... taking Fouquet's architect, landscape designer, etc, to work on remaking Versailles.
I took a direct train from Paris to the town where Vaux le Vicomte is located and then a taxi to the chateau. I went on a Saturday and stayed overnight in town, which allowed me to do a night visit and then see the fountains/gardens the next day.

One of my favorite memories of Paris with my husband was the Fat Tire Bicycle tour. It was so fun! We did the sunset tour and met at the Eiffel Tower, biked around Paris for a few hours, then the tour included a boat ride on the Seine at dusk and into the evening. At one pint we biked right onto the plaza at the Louvre just as the sun was setting and the pyramid was aglow in this beautiful coral color. The boat trip was magical as we saw Paris lit up and were on the boat for the 10 pm sparkle show of the Eiffel tower. Our guide was an American expat and was hilarious. We saw some major highlights and had a blast.