UA awards no longer have stopovers, but they offer the
excursionist perk. Because Ireland and Italy are in the
same MileagePlus Award Region, you can book your award with three legs:
...for the same price that you would have paid for SEA-DUB // FCO-SEA (the DUB-FCO leg is "free" with the excursionist perk). If you wanted to stop in DUB on both the outbound and return flights, you will only get one of the DUB-FCO legs for free (and would pay extra miles for FCO-DUB, for example). If you are on a one-way award, you will need to pay for both SEA-DUB and DUB-FCO; it's no longer considered a one-way award with a stopover in DUB. If you search for SEA-FCO, you might find a very long (but less than 24 hour) connection in DUB but wouldn't be charged extra for the DUB-FCO leg.