I see the heat pump hype shaking my head thinking how people long ago use to build with mud and made walls 2-3 meter thick. It takes the entire winter/summer for the climate to get in.

The Amish hang wet bed sheets in front of the window (with a tob under it to recycle the water) not sure how well this works in the Netherlands with 95-99% humidity, it certainly wont raise humidity but evaporation might be shit.

Not every bathroom is fit for it but if there is no AC and things become unbearable I put the shower head upside down so that the ceiling and walls get wet and it rains everywhere. Then I daisy chain fans to "tunnel" the air into the bathroom. The temperature drops like a rock.