Edinburgh is a fine base for half- and full-day trips. Glasgow is fifty minutes away by direct train and a complete change of pace — Victorian industrial city, Charles Rennie Mackintosh, world-class galleries. East along the coast, North Berwick is a Victorian seaside town with two ruined castles and the Bass Rock offshore. Across the Forth Bridge in Fife, St Andrews combines an ancient university, cliff-top cathedral ruins and the home of golf, while quieter Culross is the most complete 17th-century burgh in Scotland. South into the Borders, the abbey town of Melrose sits below the Eildon Hills with Sir Walter Scott's house, Abbotsford, just downstream.
For longer days out, the bus tours to Loch Ness, the Trossachs and the Highlands are well organised but cover a lot of ground in a hurry — better to set aside two or three nights if you want to see those properly.