• Sites that are not usually open to the public or have areas not usually open to the public, but have some significant architectural features and/or have historical, social or cultural significance to the city
• Sites that are open to the public but have some significant architectural features and/or have historical, social, or cultural significance to the city (eg. churches, theatres, sports facilities)
• Sites that can commit to opening their doors from 10 a.m. - 4 p.m.
• Sites that are celebrating significant anniversaries
• Sites recognized by heritage, urban design and/or architectural awards
• Sites with significant original interior features and/or successful adaptive features
• Sites that feature contemporary design excellence and/or innovative green/sustainable elements
• Sites in destination clusters (several venues in one area)
• Sites representing the cultural diversity of Richmond Hill
• Sites that can provide enhanced or thematic programming and/or entertainment

The first Doors Open Day (La Journée Portes Ouvertes) took place in France in 1984. The idea soon spread to neighbouring countries. In 2003, all 50 signatory states of the European Cultural Convention participated in European Heritage Days.

In 2002, the Ontario Heritage Trust launched Doors Open Ontario, the first provincewide event of its kind in Canada, attracting visitors to unique heritage sites and cultural tourism experiences. The Doors Open concept continues to spread across North America.

Since the program was launched in 2002, over 8.3 million visits have been made to heritage sites participating in this exciting initiative.