A recently published video by the Russian Air Force shows the destruction of an Al Nusra head quarters building. Al Nusra (Al Qaeda splinter cell/offshoot) is a terrorist organization that recently changed its name to Jabhat Fateh al-Sham to try and avoid being targeted by the rejuvenated Al Qaeda air strike campaign the Americans are conducting in the Middle East.
The video shows the Russian Air Force monitoring a fairly reinforced structure up against a hill/mountain. The air strike itself looked like it completed the mission but the bombs did not look they penetrated. Knowing a few tactics and the positioning of the building in the video, the terror group targeted is likely to have reinforced tunnels designed to be redundancy in the event their HQ is bombed. This has been done in just about every city a terrorist group controls.
The terrorists are an easy target and they know, if they take land from a government, that government will bomb them.