Situated about 150 km from Sofia, Plovdiv is the number one day tour destination visited by tourist in Sofia. Being over 8000 years old, it's one of the first settlements in Europe and the most important cultural centers of the region. It now has a population of about 400 thousands.
The city was originally built by the Thracians, but in the antic times it was mostly ruled by the Romans and Greeks. In the middle ages, Plovdiv kept its important status and was being ruled back and fort by Bizant and Bulgaria. During this time, Rome built lots of structures that are now an integral part of the city and make the most important sights, such as the Roman Theatre, the Ancient Stadium and the Roman forum. Other important sights in Plovdiv include the Balabanov House, the Ethnographical Museum, the Eirene Residence and the Nebet hill.
From the 14th century till the mid 19 century, Plovdiv was ruled by the Ottoman Empire, up until it finally became the part of the Principality of Bulgaria in 1885. Plovdiv was the center of the Bulgarian National Revival, which freed Bulgaria from the Ottoman Empire and so a lot of important and very interesting history was made here. It's really a pleasure to hear it from a professional guide that will give you all the details about the war that ended in the creation of the new Bulgarian state.
There are many tour operators in Sofia offering day tours to Plovdiv. Many include other destinations in the itinerary such as Koprivshtitsa or the Bachkovo Monastery, or include food and while tastings of the region. This options influence the tour price but also the available free time in Plovdiv, so be sure to check out all the options before deciding.