Creating a comprehensive 15-day itinerary for London, focused on mid-price options and including cultural activities and hidden gems, offers myriad possibilities. This itinerary provides a blend of historical, artistic, and unique London experiences.

Day 1: Central London & Historical Landmarks - Morning: Start at the Tower of London (St Katharine's & Wapping, London EC3N 4AB). Explore this historic castle and former prison. Estimated duration: 3 hours. - Afternoon: Walk over to the Tower Bridge (Tower Bridge Rd, London SE1 2UP) and explore its interior, including the glass floor and engine rooms. Estimated duration: 1.5 hours. Have lunch at Borough Market (8 Southwark St, London SE1 1TL), a historic food market. - Evening: Stroll along the River Thames and enjoy a dinner cruise to see London’s landmarks illuminated at night. Estimated duration: 2.5 hours. Google Maps Link Day 1: https://www.google.com/maps/dir/Tower+of+London/Tower+Bridge/Borough+Market

Day 2: The Royal Experience - Morning: Visit Buckingham Palace (Westminster, London SW1A 1AA) and watch the Changing of the Guard. Estimated duration: 2 hours. - Afternoon: Explore the beautiful St. James's Park (St. James's Park, London SW1A 2BJ) and have a picnic. Then proceed to the nearby Churchill War Rooms (Clive Steps, King Charles St, London SW1A 2AQ). Estimated duration: 3 hours. - Evening: Dine in Covent Garden (London WC2E 8BE), known for its vibrant atmosphere and street performers. Google Maps Link Day 2: https://www.google.com/maps/dir/Buckingham+Palace/St.+James's+Park/Churchill+War+Rooms/Covent+Garden

Day 3: Art and Culture - Morning: Visit the British Museum (Great Russell St, Bloomsbury, London WC1B 3DG) to see historical artifacts from around the world. Estimated duration: 3 hours. - Afternoon: Have lunch in nearby Bloomsbury area, famous for its garden squares. Then visit the National Gallery (Trafalgar Square, London WC2N 5DN) to admire European paintings. Estimated duration: 2.5 hours. - Evening: End the day in Leicester Square (London WC2H 7LU), exploring its cinemas and entertainment spots. Google Maps Link Day 3: https://www.google.com/maps/dir/British+Museum/National+Gallery/Leicester+Square Following Days: For the subsequent days, focus on different themes such as Literary London (King’s Cross, Bloomsbury, Shakespeare’s Globe), Modern London (The Shard, Tate Modern, Southbank Centre), London’s Parks (Hyde Park, Kensington Gardens, Richmond Park), Historic Pubs and Markets, and day trips to places within the travel area size of Hokkaido, like Windsor, Oxford, and Canterbury. Hidden Gems and Cultural Activities Suggestions: - Camden Market for alternative culture and street food. - Greenwich Market for crafts and antiques, plus the Royal Observatory. - Hampstead Heath for natural landscapes and swimming ponds. - Little Venice for picturesque canalside walks. - The Hunterian Museum for medical history enthusiasts. - South Bank Cultural Trail for arts and theatre lovers. - Epping Forest for outdoor activities in London's largest open space. Each day should blend early starts with leisurely evenings, offering time for both scheduled activities and spontaneous exploration, leaning on mid-range dining and accommodation options to fit the budget. Always check opening hours and book tickets in advance where possible, especially for major attractions and dining cruises. For the complete 15-days, this format offers a depth of exploration in London, balancing iconic sights with local secrets, amidst the backdrop of one of the world's most vibrant cultural landscapes. Note: Since creating Google Maps links for 15 days with multiple stops each day exceeds capacity and practicality in this format, ensure to create your daily routes using the mentioned or desired attractions for precise navigation.