Is it permissible to pray in an unbuilt prayer area—merely a plot of land—when there is a mosque 400 meters away?

Prayer in the aforementioned musalla (prayer area) is permissible. However, it is better to go to the mosque that is further away and has a larger congregation, due to the abundance of reward and great recompense for taking many steps towards the mosques, as indicated by the Prophetic hadiths.