Vayne's Condemn says:
If they collide with terrain after being knocked back, they are dealt the same amount of physical damage again and are stunned for 1.5 seconds.
Similarly, Poppy's Heroic Charge says:
... if they collide with terrain, her target will take a high amount of magic damage and be stunned for 1.5 seconds.
So if the enemy hits a turret, inhibitor, or nexus, does it count as terrain and cause these abilities to stun the target?