More than 450,000 people are expected to attend events around the country to mark National Heritage Week.
A record 2,289 events are being held nationwide - most free of charge - as part of the initiative.
In Cork, more than 40 of the city's best known buildings have opened their doors to the public today as part of the annual Heritage Open Day.
Among the buildings this year is the Masonic Hall on Tuckey Street and Heineken Ireland (Murphy's Brewery) on Leitrim Street.
The programme also includes the recently renovated Nano Nagle Place on Douglas Street and University College Cork's Crawford Observatory.
From educational to ecclesiastical, medieval to military, every building has its own unique history and architecture, according to Cork City Council's Heritage Officer Niamh Twomey.
Ms Twomey says its a unique opportunity for the public to get a "peek inside the many wonderful buildings that are throwing open their doors for one day only".
National Heritage Week, which is in its 13th year, runs until Sunday 27 August.