The fortress was constructed on 20 acres of land — complete with underground tunnels, ventilation shafts, ammunition bunkers, canon firing bays, observation tower, sleeping quarter etc.
If you love history, this place is a treasure. I took almost an hour walking around the fortress. Wondered what life was like for the solders.
Visitors are allowed to go into one of the tunnels. If your phone doesn't have flashlight function, bring a flashlight. As I walked in the tunnel, I could feel a breeze flowing in. After more than half a century, the ventilation shaft still works perfectly.