One of my kids' favorite activities: feeding the fish at Lisbon's Vasco da Gama aquarium. We buy two small packages of fish food (sold at the aquarium) and they'll spend one happy afternoon. And the fish seem kind of happy to see them there too.
As per the request of my son, I also had to take a picture of the turtle lazily hanging around...
Hopefully the weather will improve soon (we've had a few promising days at the beginning of spring and then just a lot of rain) and we'll be able to enjoy more outdoor activities.