White Harbor is a harbor city in the North which contains the New Castle. Located south of Winterfell, it is the largest settlement north of the Neck, but the smallest among the five major cities of Westeros. White Harbor is the North's primary trade port. Its location on the mouth of the White Knife provides opportunities for trade further north.
Due to its location White Harbor has more contact with the south and there are more knights and followers of the Faith of the Seven in White Harbor than anywhere else in the North. There are some followers of the old gods, but most follow the Faith. The city has access to good fishing grounds and is also the home of many silversmiths.
White Harbor is located on the eastern shore of the White Knife. It is clean and well-ordered, with wide straight cobbled streets that make it easy to walk around. The houses are built of whitewashed stone, with steeply-pitched roofs of dark grey slate. According to a semi-canon source, there may be a cadet branch of the Starks in the city.
You can recruit a unit called "White Harbor Knight" in sets of 5 and 10s, depending on renown/honour (I think..)