will be in frankfurt next month for 5 days with my family (wife & sons aged 6 & 4)....i will be working for 3 days but will have the weekend free before we fly out....i'm looking for suggestions on where we can go around frankfurt for 2 days....

i'm open to driving up to 3-4 hours away & am ideally looking for either a mountain or lake destination....open to other suggestions as well....

would appreciate inputs from people familiar with the area....