Frankfurt is a vibrant city with a mix of modern skyscrapers and historic buildings, making it a perfect destination for a 3-day trip. Let's dive into your ideal itinerary:

Day 1: Explore the Old Town

Start your day with a visit to Römerberg, the historic heart of Frankfurt. Admire the picturesque half-timbered houses and visit the Römer, the city hall. Don't miss St. Bartholomew's Cathedral and the nearby Eiserner Steg bridge for great views of the city skyline.

For lunch, head to Kleinmarkthalle, a bustling indoor market offering a variety of local and international food options. In the afternoon, visit the Goethe House, the birthplace of Germany's most famous writer, Johann Wolfgang von Goethe.

In the evening, enjoy a traditional German dinner at one of the cozy restaurants in Sachsenhausen, known for its apple wine (Ebbelwei) and hearty cuisine.

Day 2: Museums and Gardens

Start your day at the Museumsufer, a cluster of museums along the banks of the Main River. Visit the Städel Museum for its impressive art collection, including works by Rembrandt and Vermeer. Don't miss the nearby Museum für Moderne Kunst (MMK) for contemporary art enthusiasts.

After lunch, take a leisurely stroll through Palmengarten, Frankfurt's botanical garden. Enjoy the diverse plant species and relax in the peaceful surroundings. In the evening, head to the Main Tower for panoramic views of the city at sunset.

Day 3: Day Trip to Heidelberg

For your final day, take a day trip to Heidelberg, a charming town located about an hour away from Frankfurt. Explore the historic Old Town, visit Heidelberg Castle for stunning views of the Neckar River, and stroll along the Philosopher's Walk for a scenic view of the town below.

Enjoy a leisurely lunch at a traditional German restaurant before heading back to Frankfurt in the late afternoon. In the evening, unwind with a relaxing walk along the Main River or explore the trendy district of Bahnhofsviertel for dinner and drinks.

I hope this itinerary gives you a taste of what Frankfurt has to offer! Let me know if you need any more recommendations or tips. Have a fantastic trip!