The famous rocky massif Sinite Kamani (Сините камъни, "The Blue Rocks") and the associated nature park, the fresh air and the mineral springs at Slivenski Mineralni Bani offer diverse opportunities for leisure and tourism.

The city is also known for the mineral baths at Slivenski Mineralni Bani some 12 km southeast, whose water is used to treat diseases of the liver and nervous system.

Karandila is the site of the annual Karakachani festival, organized by the Federation of the Cultural and Educational Associations of Karakachans (ФКПДК) in Bulgaria each July.

[5] Karandila is located in the nature park Sinite Kamani (Сините камъни), whose peak Bulgarka (Българка, 1181 m.) is the highest in the eastern Balkan mountain.

The area occupied by present-day Sliven has in the past been settled by the Thracian tribes Asti, Kabileti and Seleti.

It is also mentioned by Hierocles, who identifies it as one of the four cities in the province of Haemimontus, established as part of the Diocese of Thrace under Diocletian and also by Procopius of Caesarea.

In a written record from the 3rd century, the settlement was called ''Tarzhishte" and most likely belonged to the territory of the city of Augusta Traiana (today Stara Zagora).

In the ancient fortress' interior and near its eastern wall, are excavated the remains of a basilica with a baptistery, which functioned in the 5th-6th centuries.

The seat of the bishop, however, for unknown reasons, was moved to Tuida, which very likely marked the beginning of the proverbial rivalry between Sliven and Yambol.

The area of Sliven was incorporated into the First Bulgarian Empire around 705 as part of the Slav-settled Zagore, according to Tervel's treaty with the Byzantine Emperor Justinian II.

Paleoornithologist Zlatozar Boev discovered bone remains of 14 species of wild and domestic birds in Hissarlaka from the 10th-12th centuries.

As the chief priest of the Bulgarian Militia, Amphilohiy from Sliven consecrated the Samara flag in Ploiești.

In the 17th century Sliven developed as a crafts centre and also famous for the production of guns, pickaxes, iron tools.

In 1843, the first textile industrial enterprise in the Ottoman Empire was established in Sliven, with Dobri Zhelyazkov as its head.

Continuous massacres of the Muslim population and desecration of mosques were made, involving both Bulgarian and Russian soldiers and local residents.

Metropolitan Seraphim is particularly credited with saving Sliven and a number of settlements and chifliks in the region from complete destruction.

For a short period a centre of a department in the autonomous province of Eastern Rumelia before its inclusion in the Principality of Bulgaria in 1885.

It served as the birthplace of many prominent Bulgarians, including Hadzhi Dimitar, Dobri Chintulov, Ivan Seliminski.

Another notable resident is Yordan Letchkov, whose goal in the 1994 World Cup eliminated defending champion Germany.

[26] Since 2015, the mayor of Sliven has been Stefan Radev, nominated by PP GERB (2015 and 2019), re-elected with 64.75% in the second round of local elections in 2019.

In 1834, Dobri Zhelyazkov established the first factory in Bulgarian lands, thus starting industrial development in Bulgaria.

Sliven was one of the largest industrial centers in Bulgaria, playing an important role during the Bulgarian National Revival.

It has long-lived traditions in textiles, machine-building, glass-making, chemical production, and the technical and food industries.

In contemporary times, Sliven has experienced a surge in economy with increased investment, banking establishments and new industries have begun to emerge.

The wine industry, with companies such as Vinprom and Vini Sliven and about a dozen others, continues to grow as grapes are easily grown due to the climate conditions.

Light industry in Sliven is mostly devoted to textiles with many companies making wool clothing, socks, and food.

In 2024, it was reported that a gang based in Sliven had been receiving up to £200 million annually in fraudulent welfare payments from the British government.

The cavities are filled with reinforcing filler and have been left openings for natural ventilation to stop rotting processes or breedings of microorganisms.

The aim of the excavations is the final study and conservation of the architectural and archaeological monuments, and the exposure of the fortress with a view to making it one of the city's notable tourist attractions.

In 1936, a strong storm destroyed the upper wooden part, which was rebuilt about sixty years later in its original 19th century form The Sinite Kamani Nature Park is located in the Eastern Balkan Mountains.