population of the city reached 200,000. Further growth was accelerated by the construction of Katowice Steelworks, and in 1981, the population of Sosnowiec was 250,000, reaching its peak in 1987, when it was 259,000. Since then, the population has been declining. In 1992, the city became the seat of the Roman Catholic Diocese of Sosnowiec. Economy Sosnowiec is characterised by its urban dynamics, economic activity, cultural heritage, and natural environment. In recent years, Sosnowiec was further developed from an industrial centre (with mainly mining and heavy industries) into a hub of trade and services. Nevertheless, it still operates several important coal mines, steel factories and other industrial plants. Its Special Economic Zone, established in Sosnowiec thanks to the efforts of local authorities, plays a major role in attracting new businesses into the area. As a result, several companies with Polish and foreign capital opened their businesses in the city. Sosnowiec City Office was awarded the ISO 9001 2001 quality certificate for its management system for providing services for the local community. From 2006, a new trade centre Expo Silesia began hosting numerous trade shows. Activities of Artistic and Literary Society of Zagłębie Dąbrowskie prove also that Sosnowiec as an industrial centre is not only a working-class environment. Districts For Sosnowiec's 100th birthday, the downtown area was thoroughly rebuilt, to harmonise its architectural layout and give the city a more modern image. In 2004 Sosnowiec authorities and designers were awarded the Grand Prix for the rebuilding of the downtown area in a competition for the best public space in the Śląskie Provinces. This investment had been accompanied by a program designed to improve the esthetic qualities of the city, under which a comprehensive program for unifying the colors of the elevations, and advertisements entitled “rainbow city” were introduced. Among the city districts there are: Dańdówka Dębowa Góra Jęzor Juliusz Kazimierz Górniczy Klimontów Maczki Milowice Modrzejów Niwka Ostra Górka Ostrowy Górnicze Pogoń district in Sosnowiec Porąbka Radocha Rudna district of Sosnowiec Sielec Stary Sosnowiec Środula Sosnowiec Śródmieście Zagórze Points of interest There are many relics of the industrial era, especially residences of industrialists. Most of them are located outside the strict city center, on the Czarna Przemsza river bank. One of the oldest is a 17th-century castle known as the Sielecki Castle. Other main tourist attractions include: The Dietel Palace Schöen Palace and museum Oskar Schöen's Palace called also New Schöen Palace