Tallinn is absolutely beautiful in the winter. The Old Town especially feels magical and inviting with all the colourful lights, Christmas markets and layers of snow. I had such a wonderful time when I was there to do my Christmas shopping last year but be warned, walking on icy cobbled-stoned fothpaths can be treacherous. I slipped over whilst walking down the hill in Toompea, near the Riigikogu, on my way back to the hotel. The fall damaged my camcorder but luckily not my camera. Even though I was wearing good footwear at the time and was careful with my steps, it's so easy to slip over. In the city centre I saw several elderly people walking with the aid of ski poles and it's probably not a bad idea. Best to be safe than sorry. My advise, when staying in Tallinn during the winter is to base yuorself in the city centre and avoid hills. Hotel Viru is probably your best bet, located right in the heart of town.