Travel Options from Dublin to Glasgow in One day

This past July, we took the bus/ferry from Glasgow to Belfast, and at the end of our trip, we took a bus from Belfast to the Dublin airport.

--Bus from Glasgow to ferry port: I slept most of the way, but I was informed upon arrival that it was quite scenic along the coast
--Ferry from Scotland to Belfast: This was SO fun. It was like a daytime cruise ship! We drank hot chocolate and strolled around the ship, chatting with people, watching TV, playing games, etc.
--Bus from Belfast to Dublin airport: Not at all scenic; just boring highway.

Thanks for your quick reply. I appreciate your insights.

Any reason while you aren't flying directly from Dublin to Glasgow?

Rome to Rio does spout total nonsense- just looked at it, and R2R shows the Translink (which is the Scottish Citylink, it's a codeshare) bus route as using the Larne to Cairnryan alternative ferry route (spoiler alert- it doesn't) then the bus taking a deadleg from Cairnryan to Stranraer and back to Stranraer before Glasgow (spoiler alert from someone used to that route, it doesn't. The bus starts in Stranraer BEFORE serving Cairnryan). R2R also quaintly calls Belfast International airport by it's old name of Belfast Aldergrove Airport.

The ferry ride is NOT 6 hours, it is 2 hours to the port of Cairnryan, then as alluded to above a very scenic bus ride up the coast before joining the main highway from Ayr to Glasgow- a 2 hour ride.

Hannons run a daily through bus from Belfast Grand Central Bus Station. You load your luggage on at Belfast, ride literally on and off the ferry on the bus, and retrieve your luggage at Glasgow.

It is a wonderful ferry ride, in sight of the coast almost all the way, a restaurant, bar and even a movie theatre (yes, really) on the ferry.

The bus ride from Edinburgh to Glasgow is just freeway, not without interest and seen from a double deck bus, but certainly not worth the divert to Edinburgh airport.

Option 4 would be the great value rail and sail ticket. Bus Belfast to Belfast port, get yourselves on and off the ferry, connecting bus at Cairnryan for the scenic run to Ayr, train Ayr to Glasgow Central. It is fantastic value, being less than the cost of the ferry alone.

A ferry ticket is £46 single, for me I have a 3 1/2 hour train ride first to Ayr but the through ticket with a railcard is £29.30 (railcards only valid via Cairnryan, not Holyhead). To Glasgow sail rail is £36 or £23.95 with a railcard. So you pay £10 less for your ferry and get the two bus transfers and the train for free.

Option 5 would be early ferry at about 0730 to Holyhead in Wales, train to Warrington or Crewe, change for Glasgow. A scenic run across North wa!es, and then through the Lake District and southern Scotland. Again you can book very cheap through rail sail tickets. The overall train ride is between 4 and 5 hours.
At Dublin there is a shuttle bus to the port from the City centre.
Either sea route is cheaper than flying city centre to city centre after the add on fees and the transportation costs at either end.

A single ferry ticket Dublin to Holyhead is £40, a rail/sail Dublin to Glasgow is £54.70 (£48.90 on some services) so the train fare is essentially £14.70 or less.

PS- You can take the train to Larne then walk straight on to that ferry, but there is no express bus connection from Cairnryan to Glasgow, and the local bus services to Ayr for Glasgow don't mesh well with the ferry timetable, so that route is not recommended unless a user was going to rent a car at Cairnryan, or wanted to take a taxi the 3 miles into town for the train from Stranraer to Glasgow.

We flew between Dublin and Glasgow. It’s easy.

Thank you everyone for sharing their travel wisdom.
I failed to mention in my first post that although flying directly from Dublin to Glasgow may be simple and straight forward, I would welcome the chance to see more of either Ireland or Scotland if there are reasonable (1 day) routes that offer more sceneries.
As such, Option 5 (traveling from Dublin to Holyhead, Wales then by train to Glasgow with transfer at Warrington or Crewe) provides the most interest to me. I have not been to the Lake District but have read a lot about the beautiful scenery it offers. Also the Scotland tour does not cover the southern part of Scotland. May be the train ride will offer a glimpse of that part of Scotland.

I got on the Rail and Sail website but find it not so easy to navigate around. Can I buy the rail part of the trip through the same website? Or do I have to call them like they suggested on the front page? How far ahead of time do I have to book the ferry & train ticket package before the trip?

I am thankful that this travel community is full of helpful, experienced travelers to help me figure it out.

In recent years I just buy a Sail rail ticket minutes before the train departs.

That is a little bit harder on a single ticket from Ireland where you have to collect the ticket at the port check in desk. But a day or two will be ample or anything up to 8 weeks beforehand.

On the rail sale website, to keep things simple, scroll down to the bottom of the page.

Then start inputting 'Dublin' and you will be offered various- choose Dublin Ferryport to be on the 0805 Irish Ferries sailing, or Dublin Stena Line to be on the 0815 Stena Line sailing. Honestly both ships are grand ships and it is totally invidious to choose between them. I am in the Stena frequent sailor club, so of course favour them, but that is my bias.
Then start to input Glasgow and choose 'Glasgow Central' from the drop down.

The two ships connect into the same trains- either change at Chester and Warrington to arrive at Glasgow at 1800, or wait a bit longer at Holyhead and take a train straight to Warrington, for connection to Glasgow arriving at 1917.

The beauty is that you are free to take any onward train- it is not a train specific ticket, but you will have reserved seats on whichever train you choose at time of sale.

That link takes you to the Trainline who charge about £2 commission, and is the simplest way. Personally I would book it on the Northern Rail website or the Transport for Wales website, because I'm just cheap and don't want to pay the commission.

Thank you for the instructions in your reply, isn31c!
Since the tours will be in September 2025, I will wait until August to book the Rail Sail package ticket. I am looking forward to preview the beautiful coastline, countryside of NW Wales and England's famous Lake District even though it will be from the train.

The Man in Seat 61 has pretty comprehensive information about the ferry links between Ireland/NI and UK, including photos and videos. The way his site is organized, though, routes everything to/from London, which can be a bit confusing when you're not going to London. Here is a link:
https://www.seat61.com/train-and-ferry-to-dublin.htm