Aviemore is the working town of the Cairngorms: a long, straggling main street on the old A9, a railway station, supermarkets, gear shops, and a lot of people in waterproofs. It grew up around a railway junction in the 1890s and turned into one of Scotland's first ski resorts when the Cairn Gorm chairlift opened in 1961. The concrete Aviemore Centre of the 1960s was an eyesore, and most of it was knocked down around 1998. Nobody comes here for the architecture.
You come for what is around it. The Spey runs along the east side of town, and beyond it the pinewoods of Rothiemurchus climb towards the plateau. Loch an Eilein and its island castle are an easy bike ride away. Loch Morlich has a sandy beach 300 metres above sea level, and higher up the ski road you reach the reindeer herd and the base of Cairn Gorm. The Cairngorm Mountain Railway has had long closures since 2018, so check before you plan around it.
Right behind the town, the birchwoods of Craigellachie give you a proper hill walk without needing a car. In summer, steam trains on the Strathspey Railway leave from platform 3 of the mainline station. Even in the middle of a housing estate there is a Bronze Age stone circle.
Aviemore is on the Highland Main Line between Perth and Inverness, and the Caledonian Sleeper from London stops here. That makes it one of the few places in the Highlands that works well without a car. It's a base, not a beauty. Stay a few days, use the buses and the bike paths, and the town won't matter much.