Craigellachie is the hill directly west of Aviemore, across the A9. It has been a national nature reserve since 1961. The reserve covers 257 hectares of the Monadhliath slopes and is mostly old birchwood, one of the largest stands left on Speyside, with rocky crags, small lochans and blaeberry heath higher up. It is also nationally important for its moths.
The trails start near the Old Bridge Inn and climb through the birches past a couple of lochans to viewpoints over the town and across to the Cairngorms. It's the best short walk you can do from Aviemore without a car, and an hour or two is enough.