Is usually heavily guarded, but sometimes vulnerable to stealth attacks and guerilla tactics. However, stealth attacks can be met with great retribution at a later date.
The Khyber Pass in History
Alexander the Great was particularly preoccupied with invading the Khyber Pass.
About 2000 years later, the British were obsessed with going up the Khyber Pass to advance the glory of their empire.
How to successfully navigate the Khyber Pass
Send a spy in first to gain information about the presence of dark soldiers
Make sure your expedition has the necessary supplies. Food, water, and adequate shelter are a must. Weapons might also be useful, depending on the number of dark soldiers.
Have a viable exit strategy before you attempt an invasion. You don't want to end up stuck in the Khyber Pass until all your supplies run out and your troops die around you, one by one.
