Grateful to posts about places to visit; this one is not often mentioned anywhere, but we found it well worth an overnight stay.
Stara Zagora has a very long history, and some magnificent Roman remains very near the town's main shopping and administrative area.
Just off the centre is a superb old mosque, built on the site of a former early Christian place of worship, which has been converted (very sympathetically) into a "Museum of Religion" where the history of the site can be traced and hence the basic story of the town's heritage. A very ploeasant and knowledgeable lady is available for guided tours, and there is a wealth of information.
On top of that, there are some very good eateries and bars, and a couple of really good hotels (including the Forum, where we stayed).
It's en route between Plovdiv and Bourgas (or Varna), so reasonably convenient to get to and from (we used coach and train).