McKenzie Baths is having their open day on Saturday November 20 where they will be offering entry for free. The normal fee for the pool(huttcity.govt.nz) is $5 for adults and $3 for kids.
The latest forecast says it will be 15c and showers so probably not what I'd call pool weather however the pools are heated.
Via Free'n'Cheap Wellington(us2.campaign-archive2.com)