In reply to Pietrach:
If you're staying at the Hydro, the obvious one from the front door is round the Knock (which is the hill upon which the Hydro sits. The full walk round is 2.4 miles, up a bit and down a bit, and you can go to the lower top which has a topograph pointing out all the local views. In good weather, there are views west as far as Ben More and Stob Binnean, and south-eastish to the Lomond hills in Fife. There are occasional sightings of red squirrels.
A little further afield, but still in Crieff, would be Laggan Hill and Lady Mary's Walk. Starting at the Taylor Park car park, you can go up the hill first and descend with decent views, and walk back by the River Earn along the tree-lined Lady Mary's Walk. All told, about 3-3.5 miles. Again, red squirrels are possible.
Further to the west, there is a pleasant circular walk in Comrie, which takes you up and down beside the River Lednock, including the falls at the Deil's Cauldron and the Wee Cauldron. If you do go to Comrie, visit either Hansen's Deli in Comrie, or Comrie Croft (between Crieff and Comrie) for coffee and cake.
The Crieff Tourist Information Centre on the High Street should have a leaflet with maps of local walks, but if you'd like to research beforehand, it's the Crieff Path Network leaflet link given on this page:
https://www.pkc.gov.uk/article/15382/Crieff-Path-Network
Edit - I've just looked the map to which I linked. The Knock path shows part of the walk leaving the Knock and crossing the main road (south-eastish dotted section). I wouldn't bother with this bit - it's not remotely interesting and I can't really understand why it's included. Stick instead to the main main track on the south east side of the hill, marked as the purple dashed line.
Post edited at 16:05
