The closest point from Seoul to the DMZ is the city of Paju, which is located approximately 20 kilometers (12 miles) away. Other parts of Seoul are farther from the DMZ, such as the city center, which is about 50 kilometers (31 miles) away.
It's worth noting that the DMZ is a highly restricted area and access is tightly controlled by both North and South Korea. Visitors are only allowed to enter the DMZ through organized tours, and access to certain areas may be limited for security reasons.