Hogwarts is hidden to Muggles
One of the first bits of information I learned as a student at Hogwarts is that the beloved school is hidden from those that are not magically inclined. If a Muggle was to look at Hogwarts, they would see an old ruin with a sign that reads: "DANGER, DO NOT ENTER, UNSAFE". While this seems a little dramatic to some wizards, others argue that this enchantment is necessary for the protection of the school and its students from unwanted Muggle attention and the Muggle world as a whole.
As far as my then Headmaster Phineas Nigellus Black was concerned, Muggles should not have the privilege of studying at Hogwarts, no matter their magical abilities. This opinion was highly favoured among pureblood wizarding families but was frowned upon by most everyone else, contributing to his unpopularity. He has been credited with appealing to the Ministry of Magic on more than one occasion, attempting to gain permission to ban Muggle borns from being educated at Hogwarts. His appeals, however, were unsuccessful as the Ministry ruled that all persons that possesses magical abilities are to be treated equally.
For the longest time I wondered how Muggle children studied at Hogwarts if they could only see the run-down ruin with the sign of impending doom upon their arrival. This question was answered for me when I overheard a Prefect explaining the enchantment to another student, saying that it was placed with the ability to sense a magical being. As a result, a muggle born witch or wizard would not activate the enchantment because it can sense their magic.
That being said, there were instances where the enchantment, for whatever reason, excluded Muggle born witches and wizards from seeing and entering Hogwarts. When it was discovered that the excluded were Muggle born, suspicions were raised among witches and wizards alike. They suspected that my Headmaster had taken matters into his own hands and had gone behind the Ministry's back and tampered with the enchantment to prevent Muggles from attending Hogwarts.
