Oops, it doesn't look like 'Historical Centres day' is a national day..

Other days

ruby

Ruby Day
china

China Day
cursing

Cursing Day
my little pony

My Little Pony Day
promposal

Promposal Day
gum

Gum Day
polyamory

Polyamory Day
stud

Stud Day
pumpkin

Pumpkin Day
bow tie

Bow Tie Day