One nice walk through Aviemore is to An Lochan Uaine, perfect place to camp (https://www.instagram.com/p/CiKVN1EqVgk/) you can then hike up Bynack More and do any various routes from there (I did Cairn Gorm) and either walk back to Aviemore or to the Ski Centre which has a bus (check the times since they are infrequent on weekends)