Should it get too hot to wander the streets of Milan you can spend a day in of the city’s outdoor swimming pools. Know that enter the water if you’re wearing a swim cap (and obviously swim suit) but you can buy one for a relatively modest price at the entrance. If you haven’t brought a swim suit at e.g. Calzedonia,Yamamay, H&M which you can find everywhernin the city. Admissions fees are around €7-10. The outdoor swimming pools are open from the beginning of June till the end of August.
Here are the most central ones: