On October 12, 1994, after 1,468 days of drilling, the main well of Windischeschenbach in Bavaria reached a depth of 9,101 meters below the surface. The project, known as the German Continental Deep Drilling Program (KTB), aimed to explore the Earth's crust and gather scientific data. However, the drilling was halted not because of equipment failure, but due to unexpectedly high temperatures and pressurized fluids encountered at great depth. The heat from the subsurface proved to be a major obstacle. At 9,070 meters, the temperature was measured at 256°C, and scientists estimated it to be around 265°C at the bottom of the well—far higher than predicted by existing geological models. The KTB-HB well, the main project of the KTB, was launched on October 6, 1990, and drilling took place over nearly four years in the hills of Oberpfalz. A tall drilling tower, 83 meters high, marked the site. The well was cased from the surface down to 9,031 meters, while the remaining depth to the bottom remained open. Scientists from the German Research Centre for Geosciences (GFZ), the project's operator, recorded these extreme temperatures and noted that the heat gradient—28 K/km—was significantly higher than expected. Measuring this heat was complicated, as the temperature profile had not reached equilibrium even two to five years after drilling stopped in 1994. The high temperatures and pressurized fluids made drilling increasingly difficult. At these depths, the rock could become soft enough to jam the drill string, making each additional meter uncertain and expensive. This is a technically plausible explanation for why drilling stopped, though it was not officially declared as the reason. The KTB-HB well is now filled with water and is still used by the GFZ for research, particularly in the field of geothermal energy. The heat that once stopped the drillers in 1994 is now of interest to scientists seeking to harness it for energy production. The KTB project was once the largest geoscientific project in Germany and has left a lasting legacy. Between 1996 and 2006, the site continued to be used for experiments and technological development, with 233 cable operations and over 1,000 kilometers of logging conducted. This amount of data collected in the decade after drilling stopped was equivalent to all that had been accomplished during the seven years of active drilling. Today, a lost probe with its cable prohibits any instrument descent below 6,700 meters, but the well remains an important site for scientific study.