"Create an elegant, hand-drawn illustration for the cover that showcases the timeless charm of Philadelphia. Feature a detailed sketch of iconic landmarks like the Liberty Bell, Independence Hall, and the Philadelphia Museum of Art, layered with historical elements like the American flag and stars. The title Adult Travel Guide to Philly should be prominently displayed at the top in a bold, vintage-style font, with the subtitle A Historic Coloring Book for America's Celebration in a more refined, cursive font beneath it. Use a monochrome palette with subtle shading to create a classic, yet celebratory feel, leaving ample space for the reader to interact with the design."