Gelsenkirchen is a very old city, and Buer is its oldest section. It was first mentioned in historical documents in 1003. In 1448 the Elector Diedrich of Moers bestowed "independence" on the parish of Buer, an act symbolised by a rooted lime tree in its coat of arms, and presented it with the charter of a city, which was renewed in 1922. Around 1100 the "Horst im Bruch" moated castle was recorded as being owned by the aristocratic von der Horst family, which steadily consolidated its land holdings until 1557. The district of Horst was amalgamated with the cities of Gelsenkirchen and Buer in 1928. Today some 280,000 people live in Gelsenkirchen. Since 2001 the Arena AufSchalke has been Gelsenkirchen's most prominent landmark, but it is not the only place of interest. Developed on the site of the former Nordstern colliery, the Nordsternpark offers a variety of recreational activities. One attraction is "Deutschland Express", the largest model railway in the world. The amphitheatre in the Nordsternpark, which was built on the spot where coal barges used to be loaded and unloaded, provides seating for 6,100 visitors and is a fine setting for all manner of events, while the climbing walls of the German Alpine Club are a paradise for mountaineers. The Nordsternpark is one of the main attractions along the Route of Industrial Heritage. Another historical site is Horst Castle (Schloss Horst), which was built between 1555 and 1573 as a manorial residence. Despite continuous maintenance work, however, the building steadily decayed over the course of the centuries. The castle was acquired by the City of Gelsenkirchen in 1988, and following extensive preparatory work refurbishment began in 1995. Eventually, it reopened in 1999 in all its former splendour and now serves as a centre of culture and local government. Its splendid glass hall offers an elegant atmosphere for cultural events. Another Gelsenkirchen contribution to cultural scene in the Ruhr is offered by its music theatre (Musiktheater Gelsenkirchen), one of the most spectacular theatres built in the post-war era. The amalgamation of architecture and fine arts was and still is sensational, and the contrast between light and dark and harsh rectangular and soft circular shapes proves fascinating for every visitor, as do the remarkable moving mobiles. The Ruhr Zoo is loved by children and adults alike. Founded in 1949, it quickly developed into an attractive and popular destination for a day out. Today the zoo is one of the biggest leisure complexes in the region, covering an area of about 22 hectares, and provides an insight into the life and behaviour of some 700 animals belonging to 120 different species. The zoo is being extensively modernised at the moment. Upon its completion in 2007, the "ZOOM World of Adventure" will focus on Africa, Asia and Alaska, with animals living in conditions approaching those of their natural habitats. The zoo is open 365 days a year. Gelsenkirchen Science Park (Wissenschaftspark) is a metaphor for the structural transformation of the region. Its architecture and programme symbolise a new sense of direction as the Ruhr moves into a new era. Future-oriented businesses have sprung up on the premises of a former steelworks building. Every evening a magnificent 300 metre long glass wall is illuminated by a curtain of blue-green light for about two hours after sunset. To the south of the Science Park lies the Rheinelbe Park, which used to be the site of one of the region's largest coal mines. The once forbidden territory is now a haven of art and nature, and the place where the artist Hermann Prigann implemented his concept of a "forest of sculpture". Solar energy is all the rage, and the "Solar City of Gelsenkirchen" is a project jointly run by the city council and the Science Park. The campaign promotes the process of structural transformation away from the coal and steel industries towards the forward-looking technology of solar energy. The objective is clear: environmental protection and secure jobs for Gelsenkirchen. Finally, climbing the "Stairway to Heaven", which affords magnificent views from the second-highest spoil heap in the Ruhr, is an ideal way to end any excursion through Gelsenkirchen's industrial heritage.