The city of St. Louis was built upon a complex of natural caves. These caves under St. Louis had been important in the economic development. They contributed to make the brewery industry popular since the early 1800s before the advent of refrigeration. Underground caves are naturally cool, which was especially attractive to brewers. In the caves, the temperature is maintained stably from 50 to 60 degree throughout the year. German brewery companies had taken advantage of the caves for lagering beer and for beer storage in the early 1900s. The companies even privately used these spaces as a living room, swimming pool and a theater for their families. As the industries changed, the secret spaces were forgotten. However, for a long time, the existence of the underground secret spaces has stimulated people`s curiosity because natural caves might exist somewhere under the city of St. Louis.

This project proposes the process for exploring, transforming and experiencing the natural caves for the Pruitt Ego site. By finding and connecting to possible natural caves under the site, Pruitt Ego will give special experiences to people. Pruitt Ego will be a place that satisfied people`s curiosity about secret spaces.

Drilling is a process to find possible natural caves. Through three phases, the process will visualize the map of the underground space. In the first phase, 135 holes are drilled by drilling machines. Each drilling is an examination to check whether there is a void under each drilling point. If a void is found, the point is marked and additional drilling will be conducted around it in the next phase. In the second phase, denser drilling is conducted around the holes where the void is found. The final phase repeats the examination in further detail, and the result would be used to make a map of underground space. The trace of natural caves is the starting point to build a structure on the ground over the natural caves.

The structure on the ground level has a different shape as the shape of the natural caves is determined in the drilling process. By installing poles at the drilled holes, the site above ground reflects the shape of the underground space below. Every pole has a light at the point so this site can visually interact even at night. Above the natural caves, there is the middle space between the natural caves and the ground. The space has three entrances from various directions. The space has a roof where poles are installed, and the poles function to project the shape of the natural caves visually. The light at each point of the pole helps people recognize the cavelike shape of the roof. There are two paths which people can directly go down into the natural caves. Several tubes connecting the natural caves have fans making winds from the underground.

The space gives three major experiences: stable temperature, light and a cavelike shape. First, fans installed in tubes make airflow from the natural caves. Cool air comes up in summer and warm air comes up in winter. It makes the spaces have stable temperature. Second, natural light goes to the underground space via drilled holes which have fiber-optic cables. Also, the cavelike shape is made by poles which have different heights at the roof.