Barcelona is superb. It's got whatever you want. (Good beaches, quiet bars, lively bars, nightlife, fantastic restaurants with great Catalan paella, world class museums, stunning architecture, a cheap, clean & fully-integrated public transport system and a shopaholics paradise):
http://www.barcelonaturisme.com/
(Click 'English' on the top line)
Jet2 fly from Glasgow International to Barcelona El Prat:
http://www.jet2.com/
I see that Prague is suggested above. It's also a great destination. However Wizzair no longer operate on that route from Glasgow. Jet2 fly to Prague but they only fly on Thursdays and Sundays, so you'd have to make it a 3-night break.