As part of 'Visit Wales' Year of Discovery, 16 Cadw sites across Wales will have free entry to the public on St. David's Day, Friday March 1st.
Free sites in North Wales are -
Beaumaris Castle
Caernarfon Castle
Conwy Castle
Criccieth Castle
Dolwyddelan Castle
Harlech Castle
more info via https://cadw.gov.wales/about/news/60108729/