If it's raining cats and dogs, why not spend some time at Het Prinsenhof? You'll be fascinated by just how much you can discover about the past here.
You'll be spoiled for sightseeing choice when spending time in Delft. Het Prinsenhof is a great place to begin here, but there are lots of other worthy spots to visit. Peace Palace, Binnenhof, and Noordeinde Palace are near the collection of historical artifacts and will top off your day nicely.