Here's a suggested itinerary for 6 days in Mexico City:

Day 1: Arrival and Exploration

• Arrive in Mexico City and check into your hotel
• Head to the historic center of the city and explore the Zocalo, the main square
• Visit the Metropolitan Cathedral and the National Palace
• Take a stroll through the pedestrian street of Madero and enjoy some street food
• End the day with a visit to the Palacio de Bellas Artes, a stunning art deco building that houses a theater and museum

Day 2: Teotihuacan and Frida Kahlo Museum

• Take a day trip to the ancient city of Teotihuacan, located just outside of Mexico City
• Explore the pyramids of the Sun and Moon, and climb to the top for a breathtaking view
• Return to the city and visit the Frida Kahlo Museum, also known as the Blue House
• Learn about the life and art of the famous Mexican artist, and see some of her most iconic works

Day 3: Chapultepec Park and Anthropology Museum

• Spend the day in Chapultepec Park, one of the largest urban parks in the world
• Visit the Chapultepec Castle, a historic palace that now houses the National Museum of History
• Explore the park's many gardens, lakes, and museums
• End the day with a visit to the National Museum of Anthropology, one of the most important museums in Mexico and home to many artifacts from pre-Columbian civilizations

Day 4: Xochimilco and Coyoacan

• Take a boat ride through the canals of Xochimilco, a UNESCO World Heritage Site
• Enjoy the colorful boats, floating gardens, and live music
• Afterward, head to the charming neighborhood of Coyoacan
• Visit the Casa Azul, the former home of Frida Kahlo and Diego Rivera
• Explore the cobblestone streets, markets, and cafes

Day 5: Street Art and Food Tour

• Take a street art tour of the city's vibrant murals and graffiti
• Learn about the history and culture behind the art
• Stop at local markets and street food stalls to sample some of Mexico City's famous cuisine
• End the day with a mezcal tasting at a local bar

Day 6: Day of the Dead and Shopping

• Visit the Mercado de Jamaica, one of the largest flower markets in the city
• Learn about the traditions and symbolism of the Day of the Dead, a Mexican holiday that honors deceased loved ones
• Shop for souvenirs and gifts at the colorful markets of La Ciudadela and San Angel
• End the day with a farewell dinner at a traditional Mexican restaurant

Of course, this itinerary is just a suggestion, and you can customize it to your interests and preferences. Mexico City has so much to offer, and six days is just enough time to scratch the surface of this vibrant and fascinating city.