A Longboat Key mansion hit the market at $12.9 million this week. The nearly 10,000-square-foot complex at 3105 Gulf of Mexico Dr. was built in 2004 and includes five bedrooms, six full baths and three partial baths on a 0.62-acre lot. The listing follows several multi-million mansions that have sold in the area's luxury market for record or near-record prices this year.