Any Suggestions for Indoor Activities in Berlin?

In the two forecasts below, one of these places in the middle of summer. The other is in the middle of winter. 

Glorious Berlin Summer

Rubbish Perth Winter

Vicky and I have some friends visiting from Perth this week. It's been piddling down pretty much the entire time they've been here. I'd like to blame them for the horrid weather, confusing the seasons, especially when last week was a little bit hot and I even wore shorts outside the house for the first time since leaving Dubai in January. I'd just be trying to stop myself from feeling so guilty, however, that their trip has been so disappointing. It's making it really hard to recommend afternoons in Prater, or Mauerpark, or the Tiergarten. Good one, Berlin.

There'll Be a Hot Time in the Town of Berlin

you know, I'm pretty sure weather.com is having me on, here

finally

It is about mother flipping time. We are two-thirds through spring and here is the first real run of warmish weather. In other news, I hear it is rainy in Perth today. It's almost as if we've swapped weathers. I'm pleased.

I think Vicky and I will get some takeaway margaritas, some beers, some icecream and sit in the sun. We might also play public ping-pong. Oh yeah, it's a thing here.

I'm in a jolly good mood.