A Link to the Past
The Bumper first appears within the Tower of Hera, located in a large room with a number of Hardhat Beetles. The actual bumper is completely stationary and even if Link runs into the bumper, no damage will be done.
What makes the Bumper an obstacle for Link, is that touching the Bumper causes him to ricochet quite a distance away. This can launch Link directly into other enemies, as well as sending him down into the abyss. Furthermore, combined with other enemies such as Hardhat Beetles, which also cause Link to ricochet away when he slashes at them, Link can find himself bouncing back and forth between enemies and the bumper.
Not only can Link bounce off the bumper, but other enemies can as well. Bouncing off a bumper could send an enemy directly back at Link.