Excellent and unique experience. There is so much to see, I recommend buying the guidebook to take home. It has great photos and information about all the chambers and sculptures, and also the town of Wieliczka.
Very nice way to see the southern Polish countryside and mountains. Niedzica Castle is fairly small, with narrow passages and small rooms. There are great views from the top. The river raft ride is a unique experience. Beautiful views along the river of limestone and soapstone cliffs, the Three Crowns, and occasional small villages along the way. Bring a jacket to use as a seat cushion or to wear if you get chilly. The wooden seats on the boat get uncomfortable after sitting for so long, and it can get a little chilly out on the water, even when it is warm on shore.