Is Makkah Al-Mukarramah the place of miracles, because I always heard from those who just come back from Hajj and Ummra' a miracle that happened to them and to another people?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Miracles are extraordinary favors that Allah grants a pious man to satisfy some need related to this life or the Hereafter. It should not contradict the Sharia, such as people claiming to have seen Allah and He has made prohibited things lawful to them, or that He has freed them from performing obligatory acts.
On the other hand, the granting of a Karama (miracle) is not limited to or designated for any given place or to any particular time. It occurs when there is a need for it and Allah desires it. Also, the fact that Allah causes these extraordinary acts to be performed by someone or have him receive them does not necessarily mean that this person is better than other people or that he is any closer to Allah. The opposite might even be true. As for the Karama that people report after Hajj, there is no harm in believing that occurred if they meet the conditions clarified earlier and if those who report them are known to be sincere in what they say.
Know also that real pious people do not boast when Allah performs the miracles through them, nor do they yearn for miracles. Their only concern is to follow the Qur'an and Sunnah in every way possible.
Allah knows best.