The physical feature that stretches between two bodies of water and seems to be a northern border of Muslim lands is the Caucasus Mountains.

Here's why:

* Bodies of Water: The Caucasus Mountains run between the Black Sea to the west and the Caspian Sea to the east.

* Muslim Lands: The Caucasus region is home to several Muslim-majority countries and regions, including:

* Azerbaijan

* Dagestan (Russia)

* Chechnya (Russia)

* Ingushetia (Russia)

* Northern Caucasus (Russia)

* Parts of Georgia and Turkey

While the Caucasus Mountains are not a definitive border for all Muslim lands, they are a prominent geographical feature that does mark a significant part of the northern boundary of the Islamic world.