No shortage of good long hikes in the Cairngorms, but remember it can be awful wild if you're going up into the hills even in the summer. Indeed it can be awful wild even if you're wandering through the glens in the Cairngorms!

There's some good ideas/routes on this site, depending on what you're after. Covers most options from gentle wanders to serious expeditions.

Might be worth a wee look for ideas.