Germany's weather has multiple personalities. A sunny summer day can be overtaken by a rumbling…read morethunderstorm in mere moments...a freak warm day can surprise even the most tuned out local if it happens in early spring or late fall. I've been to Wonnemar on both of these kinds of days...and, left happy and relaxed both times. Part kid water park, part adult spa, Wonnemar itself has multiple personalities. And, multiple locations...seven to be exact. This one is in Ingolstadt.
For the young (or young at heart), there are indoor and outdoor pools (with lots of lounge chairs and umbrellas) and water slides. If you'd rather not be splashed, you can segregate yourself in the adult spa area and soak in one of the heated pools, cook in the sauna, or breathe deep in the salt room. (If you've never tried a salt room, this is reason enough to come here.)
Bring a towel, a bathing suit, flip flops, the price of admission, your own snacks and relax for awhile.