Unique European Trips/Destinations for Honeymoon?

Time of Year?
Have you been to Sicily? It's gorgeous with lots of culture and history. I think Palermo sounds right for you, but there are many other places worth visiting in Sicily.

Palermo? And the whole of Sicily?

You didn’t mention the month, which might affect recommendations. How about Sardinia or Puglia? Or Sicily plus its islands?

How about Turkey?

I was going to recommend either Turkey or Morocco. And for timing would travel there after.

Sardinia, Algerho in the West corner, or beaches along the Southeast coast. Many B&B's or VRBO's to choose from, great food, fantastic wineries. Pre-Covid, we rented a VBRO in late June near the beaches with its own private pool. Might bust as Sardinia ise a little pricey in August as Sardinia is where the Italians vacation. Believe it is still not on the radar of American tourists. Easy flights from Naples.

Turkey was the first thing that came to my mind when reading your post.

The Canary Islands are a surprising destination that gets little attention from Americans. Lots of recent volcanic activity which leads to fascinating geology. Interesting farming, including aloe vera. Lovely beach clubs.

Check other Greek islands and Balearic Islands (Spain), e. g. Ibiza.

The OP has been modified to include the date - August 30

Thank you all for such thoughtful responses! Definitely makes us more excited about our improvised trip! I have heard wonderful things about Turkey and have visited Istanbul - any beach towns recommendations?

For Sicily - best areas to stay?

If I ever return to Turkey, I'd like to explore the coast west from Antalya.

Corfu is not so far. Or fly to Crete. Both are god for partying and general tourism too.

just wanted to say you must be good friends/family to give up your own honeymoon plans for someone else's wedding? congrats and may good karma come to you!

If you want an amazing trip filled with history, and scenic places, consider Egypt.
Do a tour with a Nile cruise. It is not expensive. We did a great tour with Nile cruises a couple of years ago with Gate 1 Travel.

It's important to recognize that August is "vacation month" in Europe. The Sorrento area is jammed in the summer anyway, so it won't be that "romantic" while you are there. You did say "culture-rich cities", so it's unclear if you mean places more like Sorrento/Positano. But I would get away from the Amalfi Coast at that time of year. The longer after August 30 the better.

If you want to stay in place, maybe Sardinia or Corsica. If you want to move around, Croatia. (Now I see you've been there) But these places will remain very hot, still. If you really want upscale nightclubbing, how about the Balearic Islands. (I think the Canaries are too far and too low-end touristy, also very spread-out if you want to change locations from one to another. I mean transit-spread-out, not mileage-spread out.

If you can afford it, Switzerland might be cooler. (Zurich itself is a business center, not mountain tourism.) Have you been to Prague before? There's a bit of romance to Cesky Krumlov, despite high tourism. Lake Konstanz? Besancon and tiny villages nearby?

Big mistake. Cancelling YOUR honeymoon for the sake of someone else’s wedding. And cancelling Japan. Big mistake to miss Japan. It is truly a unique destination compared to Europe. Rethink that.

Why not just hop on a plane in Rome after the nuptials and continue on to Japan? A quick google tells me ITA flies 6 nonstops per week.

Japan is amazing, but August is to be avoided due to heat and humidity. I suggest you consider Iceland, the Azores, and Northern Spain.