#Sponge down Mobility hub as a green entrance at the south portal of Karlsruhe station

The mobility transition, climate crisis and demographic change have long since reached our city centers. In this discourse, Karlsruhe Süd station square opens up to its users with pleasant and natural transfer connections between train, long-distance bus, bicycle, kiss ride and cab as well as with a wide range of offers as an urban break area for the delayed connecting train or the lunch break. In line with the concept from the winning multiple commission, a functional and atmospheric square space was created that is effective as a climate adaptation measure, complementing the north station square as a green entrance with a high recognition value.

In the difficult urban environment, characterized by the historic train station behind it, flanked on both sides by glass office towers that have fallen out of time, almost completely underbuilt with an underground car park and exposed purely to the south, the theme of the 2019 competition was obvious: a climate square with a high quality of stay, as a green calling card for the city.

The zoning resulted from the intersection of movement sequences, usage requirements and climate simulation of the existing building: two generational groves with 25 different climate trees of different plant sizes flank the recreation areas on both sides of the station portal, equipped with long benches and additional options for above-ground bicycle parking. A water feature acts as an active and playable cooling element that draws in the local hotspot of direct sunlight and reflection from the surrounding façades according to the surface temperature. At the same time, the discreet division of the fountain field in combination with the furniture forms the boundary for motorized individual traffic, which remains behind the southern edge of the square in accordance with the basic concept. There are also kiss-ride facilities for local residents and parking spaces for cabs.



Sponge underneath . Coming from the station passage, the square opens up as a three-dimensional green space: two groves of trees line the square in the common areas, offering vegetative shade, evaporation cooling and wind protection against downdraughts between the 45m high building flanks, so that a feel-good climate can be offered throughout all seasons.

Despite the almost complete underpinning of the square, surface water from the recreation areas, which are differentiated from the movement paths by a lush topography, is collected and made available to the climate trees in a 1,200m3 sponge body. Based on the classic sponge city principle, the tree quarters were designed with a solution specially developed for the urban character of the site.

In the spirit of a blue-green infrastructure, the paving, which is perforated via grass joints in the recreation areas, breathes and feeds the surface water via a system of partial seepage pipes to the connected root zone with up to 1.5 meters of cover on the underground car park. Integrated inspection shafts ensure ease of maintenance, enable scientific monitoring and ensure disaster safety by means of emergency overflow, whereby the space itself can compensate for extreme precipitation events of up to 100 years.

Specially developed light stems penetrate the tree canopies in a playful arrangement, ensuring the high requirements for glare-free illumination in interaction with the vegetation in an atmospherically independent manner. During the day, they assume an important landmark function even from the train.



Resistant urban building block

In everyday urban life, visitors can be offered a transfer and break area with a high degree of naturalness, integrated water management, real climate effectiveness and high recognition value. As an urban building block, the station square offers the young neighborhood a strong and natural place of identification and enriches the urban space as a green oasis with a new resilience to heavy rainfall events and heat waves.

Climate protection/climate adaptation awardGerman Landscape Architecture Award 2025

Jury verdict:
The initial situation was extremely poor: a south-facing urban space at the rear of Karlsruhe railway station, framed by two glass office towers that reflect the sun and cause downdraughts; the square itself is completely sealed, almost entirely underpinned by an underground car park and occupied by mobility functions.

Precise climate simulations with temperature, wind and reflection data as well as intelligent water management have made it possible to create an area for people to spend time in.

A sponge consisting of a skeleton body and special substrate creates root space for the newly planted trees. At the same time, a volume is created to absorb water during heavy rainfall events and a reservoir for dry periods. Benches in the shade of the trees invite people to linger and a water feature with a fountain that follows the course of the sun provides cooling in the summer. The project is accompanied by scientific monitoring, which analyses the effectiveness of the measures even after completion and thus provides valuable findings for comparable projects.

The project is outstanding as an open space planning conversion of an existing urban space in which climate adaptation could only be realised with a high level of technical effort. This project clearly shows that truly sustainable open spaces can only be created if the objectives of climate-adapted construction are already taken into account in the urban planning concept.