10 days in June or July, where should hubby and I go?

You haven’t told us any of your interests so it’s difficult to say where you should go. However, you might consider going in June rather than July when the temperatures in Spain can start approaching triple digits.

Most of Spain's smaller towns are not flat, they don't call them "hill towns" for nothing. I'd look into the Extremadura region, most of the towns there have a gradual incline.

My favorite cities in Spain are listed in order of preference

Seville
Toledo
Barcelona
Granada
Segovia

I didn't find the Costa del Sol that super, beaches are not that great.

For 10 days, it would be hard to see all regions of Spain. If you like the south, then do Seville, Cordoba, Granada and Rhonda.
On another trip, do Madrid (day trips to Toledo and Segovia) and Barcelona.

Ronda is beautiful and fairly flat unless you want to walk down into the gorge area - and it's an easy train ride from Madrid! We enjoyed both for several nights on a trip we took 10 years ago.

Southern Spain has many fascinating cities, but it becomes perishingly hot in the summer. Here are the June 2021 actual, day-by-day temperatures for Seville. I don't know whether last June was better or worse than average (you can go back another few years on timeanddate.com to check on that), but last year the high temperature hit 90F, or higher 16 times in June. July was far worse: It went over 90F every day, and it was over 100F eight times.

Madrid's not quite as bad as Seville, but summers tend to be unpleasant there.

For the time of year you plan to travel, I'd suggest sticking to Barcelona (and even that city is sometimes humid, so 80F can feel hotter than that) and the north. You could spend a few nights in much-smaller Girona and take a day trip to Figueres to see the wacko Dali Theatre-Museum.