Here's an ideal itinerary for 3 days in Zagreb:

Day 1:

• Start your day with a visit to the Zagreb Cathedral, one of the most iconic landmarks in the city.
• After that, head to the Dolac Market, where you can find fresh produce, local delicacies, and handmade souvenirs.
• Next, take a stroll through the charming streets of the Upper Town, where you can admire the colorful buildings and historic architecture.
• Stop by the Museum of Broken Relationships, a unique museum that showcases personal stories of heartbreak and loss.
• End your day with a delicious dinner at one of the many traditional restaurants in the city, such as Vinodol or Agava.

Day 2:

• Start your day with a visit to the Mirogoj Cemetery, a beautiful and peaceful place that is also a work of art.
• Next, head to the Museum of Contemporary Art, which features a wide range of modern and contemporary art from Croatia and beyond.
• After that, take a walk through the lush greenery of the Botanical Garden, where you can see a variety of plants and flowers from all over the world.
• In the evening, catch a performance at the Croatian National Theatre, which hosts a variety of plays, operas, and ballets throughout the year.

Day 3:

• Start your day with a visit to the Zagreb City Museum, which tells the story of the city's rich history and culture.
• Next, head to the Strossmayer Promenade, a scenic walkway that offers stunning views of the city.
• After that, visit the Museum of Illusions, where you can experience mind-bending optical illusions and interactive exhibits.
• End your day with a relaxing visit to one of the city's many thermal spas, such as Terme Tuhelj or Aquae Vivae, where you can soak in hot springs and enjoy a variety of wellness treatments.

I hope this itinerary helps you make the most of your time in Zagreb!