The Israel Defense Forces revealed on Wednesday the largest Hezbollah tunnel system uncovered during last winter’s “Operation Northern Shield.”

According to the IDF, the tunnel, originating in the southern Lebanese town of Ramiyah, was 260 feet deep—equivalent to a 22-story building—more than 3,000 feet long and extended nearly 250 feet into Israel. It featured air-conditioning, phone lines, rail tracks and staging grounds for cross-border invasions.

The IDF launched its operation in December to discover and eliminate tunnel systems that Hezbollah could use to infiltrate and attack the Jewish state.