Rotorua's Kuirau Park has a crater lake and pools of boiling mud

I know one thing it's free of charge: wandering around the Kuirau Park (west of the centre off Ranolf St). That's an area of volcanic activity and its most recent eruption in late 2003 covered much of the park in mud (including the trees). Of course, that drew crowds of spectators for more displays. But it worth a visit: it has a crater lake, pools of boiling mud, plenty of steam and small mineral baths.