Kerava Ice Hall offers free skating time for the towns people (and others) on Sundays from 11 to 12 and on Thursdays from 14 to 15.
Oh, and of course you can see some local ice hockey matches here, if that's what you're after. You should ask some local people to find out when there's a game on for you (unless you can read Finnish and check it in the local newspapers yourself).
Equipment: I don't think they have gear rental at all.
In winter time, you can go skating for free on the skating rinks provided by the city council. In this picture, they are making some ice on the sports field between the Central School (building on the right) and the Central Park of Kerava.
Equipment: You should bring your skates with you for there is no equipment rental.
This is the local swim hall and even though it doesn't look like much, it was renovated recently and I've heard people like it better than for instance the halls in some neighbouring towns.
Tickets for adults cost 3,00 eur for a morning swim (weekdays from 6 to 9) and 3,30 at other times. This price entitles you also to the use of the sauna facilities. Please remember to follow the rules. The tickets to the gym cost 4,00 eur. They have trainers should you need one and they also do physical condition testing for 10,00 eur.
There's also a small cafeteria.
* weekdays from 6 to 21
* saturdays from 10 to 18
* sundays from 11 to 18
Equipment: You can rent swimsuits.