Late spring is Uppsala at its best. The city celebrates Walpurgis Eve (Valborgsmässoafton) on 30 April with the most elaborate student festival in Sweden — bonfires, choirs in white caps, and tens of thousands of people in the streets. Book accommodation months ahead if you want to be in town for it.
Summer is short, light, and lovely: in June and July the nights barely go fully dark, the Botanical Garden is in full bloom, and the river paths fill with picnickers. Most students leave between mid-June and late August, so the city is quieter than its term-time energy suggests.
Autumn brings the strongest student life — term begins in late August, the leaves turn dramatically by early October, and the cafés get busy. Winter is cold (regularly below freezing from December through March) and dark, but the lit-up cathedral against snow is genuinely striking. December's Christmas markets and the season of student concerts make it worth braving the cold for a few days.