In short
The sauna is not a leisure activity here but a domestic habit: the country has more saunas than cars, and Helsinki's public ones — Löyly, Allas, Kotiharju — are used all year, including with a dip in the frozen sea.
The sea fortress of Suomenlinna, a World Heritage site, is reached by a ferry included in the city transport ticket.
What it really costs
It is expensive, slightly less so than Oslo and Stockholm. Housing dominates, and the rental market in the centre is tight.
Public libraries, Oodi among them, serve as free workspaces — heated, connected and open late. On a long stay that replaces part of the coworking budget.
What nobody tells you
Winter is long and dark rather than extreme: it is night by three in the afternoon in December, and snow lies from November to March.
Finns speak little, and the silence is not coldness: gaps are not filled, people do not talk on public transport, and it is disorienting for the first few days.
Ferries to Tallinn cross in two hours and sometimes cost less than a meal. Plenty of residents do their alcohol shopping there, where tax is lower.