I've never seen anything like it! Go after dark for the best experience, bundle up and pre-arrange your return ride. The taxi ranks are very busy and frozen tourists are easy pickings for drivers looking to make a huge markup on the standard fare. Nothing wrong with that, but be prepared to negotiate, hard. We had a car booked already and were very grateful as the cold had crept in. As sad as I was to leave the park behind it was a relief to get back into the warm - three pairs of cold-weather trousers were not enough to hold it at bay.
Link to my pictures of the 2011-12 event on flickr: http://www.flickr.com/photos/mlle_jordan/tags/harbininternationaliceandsnowfestival/
Also well worth a visit - the Zhaolin Park Ice Lantern Festival. A similar but smaller-scale event also within Harbin. Pictures here: http://www.flickr.com/photos/mlle_jordan/tags/icefestivalzhaolinpark/
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