Barcelona - More "modern" but more than enough to "see" and substantial ease in doing so. I suspect that Barcelona might be a one time choice, "once around the track" enough, but I can think of no more appealing city for a first and serious visit.

Oxford and environs - One of the best "one week' vacations we've ever spent was in Oxford, with several days of car rental to visit some nearby sites/attractions.

Bruges - a week may be more than needed, but allows for a couple of days in a nearby city such as Brussels or other short side trips.

Lisbon - an easy choice

Istanbul - on the edge, but European enough to qualify. It's been a long time, but it tops my list to revisit soon, even with some social and political discord.

In any case, get yourself out of the big "branded" hotels. We used to stay on "points" often, and I recall the awful realization one morning at Vienna's Marriott at the Spanish Riding School that, even with Vienna's great charm and character and the staff's accents, I might have been in Kansas City. Unlike the US, Europe has hundreds (no, thousands) of appealing small essentially "owner-operated" hotels, many modest in features and facilities (and a week with a tiny bathroom will not spoil your life), but which for a variety of reasons provide greater access to local culture, venues and activities. Reviews for "non-resort" hotels of this sort are easy to "filter", and even the negative reviews may subtly reveal good reasons to select one.