Hi there Chantel,
That's a lovely present for your hubby. A long weekend using Dublin as a hub might be most convenient due to time constraints and the proximity of many interesting historical sites. Dublin City also has much to offer itself in terms of history, culture, and other attractions.
So destinations to consider:
Newgrange is considered one of Ireland's most historical sites and is conveniently located less than an hour's drive North of Dublin. It's a passage tomb with a 5000-year history and a UNESCO World Heritage site since 1993.
Kilkenny City is a medieval city about 1,5h drive to the South-West of Dublin. You could visit places such as the Medieval Mile Museum, Rothe House & Garden, Black Abbey, and generally just soak in the atmosphere and enjoy local crafts and markets.
Glendalough Monastery is located in the heart of the lush Wicklow mountains. It is considered as the spiritual center of Ireland's Ancient East and being just an hour's drive to the South of Dublin it would suit your schedule.
Within Dublin City, take a look at sites like Dublin Castle, Christ Church Cathedral, and Kilmainham Gaol. I'd be happy to make more suggestions if you can tell me more about your and your hubby's preferences in terms of history and other activities.
Welcome to Ireland!
Best wishes,
Lauri