Hidden gems in Dublin

[Justkeepleft]

Dh has a company trip to Dublin at the end of the month.
They are looking for cool stuff to do that is not well known to tourists. Would love some tips.
TIA

There’s a costume, toy and doll collection in Rathfarnham Castle.
Malahide Castle and Gardens is easily accessible from the centre by public transport. You can tour the castle and there’s a butterfly house in the gardens. The walled gardens are lovely too. They often have exhibitions as well.
The Dublin Writer’s museum isn’t so well known.

St michans in the city centre - organ where Handel practised the messiah before its first performance, and a crypt (mummified bodies)

Thanks. They both sound great.