I stayed in a hotel near the airport (and literally adjacent to a train stop) with some interesting style:
The late afternoon flight meant a solid morning of touristing in Helsinki, seeing mainly Sveaborg/Suomenlinna.
"The Swedish crown commenced the construction of the fortress in 1748 as protection against Russian expansionism...The original plan of the bastion fortress was strongly influenced by the ideas of Vauban, the foremost military engineer of the time, and the principles of star fort style of fortification, albeit adapted to a group of rocky islands." wikipediaHanging out with a fellow mathematician means I was proudly shown the Penrose tilings in the square as we walked in some light drizzle from the train station towards the harbor. Picture on the right is a view of an island with a house on it. Not an uncommon sight in an archipelago here.

Alighting from the ferry, one sees a useful map which explains that this fortress is spread out over several islands, all joined with bridges.

The weather cycled between light rain, dry spells, and heavier rain.
Heading back to shore with the goal to find some lunch, took a slight detour to see "the church" and the view from the church. I was told the architecture is "old Russian", as Helsinki was elevated to capital city when Russia took over in 1809.
Lunch was some Ramen (with corn in it. Odd. Like Germans adding (canned) corn kernels to salad. Why?), followed by tea at a moderately awkward (or, incredibly Finnish) tea shop close to the train station, the Old Tea Shop. The selection was very good and pricing great (3.50 Euro pp, shared a giant pot of tea, and an extra 1 euro for all the tea cookies you feel like eating). Had a yellow tea (had never had before) and had the difference between teas explained a bit. Basically you have everything from the same plant, with a split between (unoxodized (= green teas)) and (partially or completely oxodized). Partially gives you stuff like Oolong. Completely gives you black and yellow.
Back to the airport (30 min by train, trains run about every 10 minutes from 9am onwards on the weekends, about 5 Euro each direction) and off to Vaasa!