Presumably you could also tunnel into the room, if it's ground-level. If not, you could also presumably break through any of the walls connecting to the room.
However, we should also presume that since this is a safe room that the walls ought to have some kind of protection.
None are explicitly stated, but Hogwarts would be a poor choice to place the stone for protection if the walls were so easy to break through.
And, if it were that easy, this would mark a flaw for every challenge presented on the way to the Philosopher's Stone.
The point of the protection, after all, is not that it keeps you out by brute force, but that if someone does try to break in, people will find out before they get past the protection placed on the stone. There are enough powerful wizards in Hogwarts that trying to blast through the walls would almost certainly alert someone to the presence of an intruder, if by nothing else than the sheer sound of the blast.