In the past, any real estate investment in the former Warsaw Ghetto area required an authorization from the conservator of monuments. Thus, when a project was to be carried out on the site of a building located in the area of the Warsaw Ghetto, a positive decision was required, but not when the ground was empty of any buildings. Today, any project, even on empty ground, will require an approval, connected with the preservation of the ground and possible archeological researches.
Update – On October 16th, the conservator of monuments also published a map showing the 28 most valuable sites in Warsaw for their archeological value.
Beautiful Warszawa 