Boston's Most Expensive Condo -- The entire 18th floor at Trinity Place is up for sale as a double penthouse unit. This 8,542 square foot Back Bay condominium includes 8 bedrooms, 13 bathrooms (8 full), and 4 valet parking spots in a luxury, 24-hour concierge building. Did I mention the panoramic views? The price tag for this residence is set at $15M.