We are going in mid-October and planning a three week trip. So far, we have:
Madrid: 4 nights (we land there the evening of our first night)
Rent a car and travel to:
Toledo: 1 night
Cordoba: 1 night
Granada 3 nights
Ronda (exploring that area) 2 nights
Sevilla 3 nights
From Sevilla we will fly to Bilbao.

I think we have one more night we can add on somewhere to this part of the trip and am hoping someone can recommend where we should add a night. We enjoy museums, historic sights, nature, strolling and eating. We aren't big shoppers. Thanks so much for your advice.

Just one night ? No big deal. Add it to Seville or better yet to Cordoba !

That's hard, but my vote would be probably be Seville (we spent 5 nights there and didn't run out of things to do), but I would have happily spent more time in all of our locations (we had 2 nights Cordoba, 3 in Granada, 3 in Madrid). I haven't spent time in Ronda or Toleda, but I know kja (who will probably chime in) was glad to have spent two nights in Toledo (but she also enjoyed her two nights in Cordoba).

You may have already done this, but have you mapped out what you want to see and do in each location? Which one seems most rushed? Alternatively, consider we're you'll be on Sunday and Monday and add a day there--as many things will be closed and you may find your sightseeing more limited.

I loved Toledo, and would probably add a night there. However, I've never been to many of the other cities, so it's hard to give advice.

Based on your itinerary, I have to agree to adding a night in Sevilla, unless you have only one night in Bilbao, then I would add it to Bilbao.

Madrid ..

No wonder I am having trouble deciding! Many different opinions here. I will go back and outline what I want to do in each location and see what seems tight.

Thank you.

An interesting day trip from Seville could go just a bit south to Jerez de la Frontera - a so-so town but with two stellar attractions- as the home of sherry (the name a British corruption of sherry as Brits took over the market as it was a favorite with Brits,, especially for older ladies) and the tours thru the caves and processing houses are nice - and practice sessions of the famous Andalusian horses - mammoth beasts that go thru their paces at practice sessions many days and performances on some.

I did this by train and also did Cadiz, a lovely seaside city.

Spent several days in Seville but feel 3 days is enough there for the average tourist.

I'd also do Cordoba as a day trip from Seville - to prevent having to relocate after just one night.

I would add a night to Toledo.

I'd add the time to Toledo. Or, if you have only 1 night in Bilbao, I agree that adding a night there would make sense. Of course, more time in Madrid and Sevilla and Cordoba would also be nice. ;-)