Miten pitäisi merkitä valtakunnan lukuisia hiihto- ja ulkoilumajoja? Niille ei näyttäisi olevan omaa tägiään. Sellaiset, joissa edes ajoittain toimii kahvila, on merkattu kahviloiksi. Monet ovat pelkkiä rakennuksia.
I’d imagine building=cabin would probably work? Perhaps in conjunction with tourism=alpine_hut or tourism=chalet depending on the use of the building. You might also consider adding sport=skiing and/or shop=ski if appropriate.
(Note: there is building=hut but I don’t think this is quite the same as what you’re intending.)
Depending on the level of amenities, amenity=shelter + shelter_type=basic_hut or tourism=wilderness_hut might be more appropriate.
The wiki pages of those tags are really well detailed, basic_huts don’t have stove, while wilderness_huts do, and alpine_huts have staff (to sum it up).
Thank you guys for helping.
Unfortunately, none of the proposed tags would be a complete match.
Those buidings are not sheds, huts, or cabins (?) as they are made of logs (diameter 20 cm). They are proper houses in which people could live or at least stay overnight also in the winter. However, these houses have limited open times. They usually belong to sports clubs which arrange club events in them. In addition, there may be temporary cafes in them in the weekends during the best skiing season in the winter. Sometimes such a house could be open for people hiking in the summer/autumn, too.
I am from Finland. We do not have any proper mountains in this country, so a vast majority of those houses are not really “alpine” buildings. They are log houses in the forest.
Any more suggestions? 
For the buildings you’re describing, I’d still use building=cabin. For more lightly constructed ones, shed might be more proper - there are some that are built using even just a single layer or wood planks.
Then just add opening hours or, in this case maybe seasons, to it. Depending on how they are available for the public, some conditional access restrictions might be in order…
By the way, we had a very similar discussion in the finnish forum in 2020 … Ulkoilumajat?
When these are run by sport clubs and they function as a club house as well I would also use …
amenity=community_centre
community_centre=club_home
club=sport
operator=*
Thank you all. This is clear enough, now.