Allah, in His Infinite Wisdom, has blessed certain places over others. As a result, one of the ways in which a person can increase their chances of their du’a being answered is by making du’a in these places.
For example, mosques are preferred by Allah over houses and market places. Likewise, the places of Hajj during Hajj time (Mina, Muzdalifah and ‘Araft) are places that the Prophet, peace be upon him, would make du’a in. Other places include the Mounts of Safa and Marwa, inside the Ka’bah, and of course the Harams of Makkah and Madinah.
It is important though, not to exaggerate in this regard, by considering places that are not blessed, such as mosques that are built on the graves of famous saints, or have such graves inside them or connected to them. Such places are not holy in the slightest. In fact, prayer in such mosques is not allowed due to the explicit narrations of the Prophet, peace be upon him, in which he prohibited Muslims from praying in mosques built over or around graves.
It is narrated that when Umm Salamah and Umm Habeebah told the Prophet, peace be upon him, about a church in which there were images, he said:
“When a righteous man died among them, they would build a place of worship over his grave and put those images in it. They are the most evil of mankind before Allah.” (Recorded in al-Bukhari)
He, peace and blessings of Allah be upon him, also said:
“Those who came before you took the graves of their Prophets and righteous people as places of worship. Do not take graves as places of worship – I forbid you to do that.” (Recorded in Muslim)