Ok , at the risk of offending any Glaswegians, it would not be my priority if I had a day in Scotland. Of course, you may have a particular reason for wanting to visit. I went to university there and my daughter currently studies there and it is hands down one of the friendliest cities in the world. The city’s slogan is “ People Make Glasgow”. The area around the university is really pretty and there’s some great free museums but a lot of it is quite rough around the edges. Glasgow is more about the atmosphere, rather than the view. It’s not the most scenic of places. If it were me I would do Stirling Castle and the Trossachs. To combine Glasgow, Loch Lomond and Stirling Castle would be quite a whirlwind tour. You can spend a whole morning at Stirling Castle, then tour the Trossachs. On the way back you would likely take the route which passes by Loch Lomond. The scenery in/near the Queen Elizabeth Forest Park in the Trossachs is especially stunning. I prefer it to Loch Lomond. I also like Loch Tay, which is a wee bit further north but a visit there would depend on timing. If you do decide to visit Glasgow and have specific questions, please ask away. I hope this helps and have a great trip.