Danakil (desert and jungle house, egapark)

Until 2021, Erfurt's egapark showed its exotic plants in a group of five connected glasshouses: the tropical house opened in 1983 and remodelled in 2007, the cactus house (1985), the orchid house (22 August 1986), the butterfly house (1997) and the Victoria house (September 1998). Preparations for the 2021 Federal Garden Show (BUGA) in Erfurt prompted the idea of a new building: a first sketch dates from 2013, and the 2015 competition was won by the ARGE Danakil team led by Henchion Reuter Architekten (Berlin and Dublin), with Rehwaldt Landschaftsarchitekten (Dresden and Prague) and the exhibition designers stories within architecture (Berlin).

The outline design and the funding application followed in 2016, the permit and tender in 2017. Construction began in 2018 and was completed in 2020 (February 2021 according to the Thuringian chamber of architects), and the building opened with the BUGA in 2021, commissioned by the Erfurter Garten- und Ausstellungs-GmbH (ega). It cost about 20 million euros; the journal Stadt+Grün gives 21.4 million for Danakil and an overwintering greenhouse, of which 15.5 million, 90 per cent of the 17.2 million in eligible costs, came from the Free State of Thuringia under the regional economic structure programme (GRW). The operators expected up to 100,000 visitors a year after the BUGA.

Danakil consists of two glazed halls, the desert house (1,250 m²) and the rainforest house (820 m²), together with a winter garden and a new footbridge, the Rendezvousbrücke. The building is 83 metres long, 30 to 35 metres wide and 8 to 13 metres high, encloses 33,000 m³ and offers 3,994 m² of usable floor area. Its designers describe it as restoring lost spatial qualities of the park by returning to the guiding ideas set out for the park in the 1960s by the landscape architect Reinhold Lingner.

The envelope is double insulating glazing with a solar-control coating. Artificial rocks and interior floors act as passive thermal mass, supplemented by mechanical ventilation with heat recovery and radiators set in underfloor ducts along the facades. The desert ranges from 12 to 22 °C depending on the season, with no active dehumidification, and its natural ventilation tolerates up to 3 °C above the outside temperature in summer. The rainforest, kept between 18 and 28 °C and 60 to 85 per cent relative humidity by high-pressure misting, has motorised openings in the facades and roof and a movable internal sunshade.

The desert holds five-metre palms and 40 large cacti from historic collections, chosen with advice from the Kakteen Haage nursery; some weighed three to four tonnes. A dune was built from 80 tonnes of fine, pale sand. The display is organised around survival strategies: plants that escape the sun by growing underground, such as Fenestraria, plants that make their own shade through their form, spines or ribs, and plants that search for water with their roots.

Animals are a major presence: elephant shrews, gundis, long-eared hedgehogs, burrowing frogs and meerkats in the desert; green iguanas, water dragons, freshwater stingrays, a tree python in an enclosure four to five metres high and leafcutter ants in the rainforest, which also has a butterfly valley and a 6.5-metre waterfall.

Danakil occupies a central position in the egapark, Erfurt's horticultural park on Gothaer Straße. The route follows the watercourse from one climatic landscape to the next, with side paths. There are no signs along the way: discovery relies on an app styled as a dowsing rod, an interactive audio guide, touchscreens and swivelling landscape scanners.

The visit extends naturally into the rest of the egapark, whose 1960s design ideas by Reinhold Lingner inspired the project; the Rendezvousbrücke links the building to the surrounding park.