Hola! Welcome to Barcelona, a vibrant city known for its stunning architecture, delicious food, and lively atmosphere. I've put together an ideal itinerary for your 4-day stay, taking into account your constraints. Let's dive in!

Day 1:

Morning: Start your day with a visit to the iconic Sagrada Familia, Gaudi's masterpiece. Be sure to book your tickets in advance to skip the lines. Afternoon: Explore the charming Gothic Quarter, wander through the narrow streets, and visit the Barcelona Cathedral. Evening: Enjoy a traditional Spanish dinner at a local tapas bar in the El Born neighborhood.

Day 2:

Morning: Head to Park Guell, another Gaudi gem, and take in the colorful mosaic sculptures and panoramic views of the city. Afternoon: Visit the Picasso Museum to admire the works of the legendary artist. Evening: Stroll down La Rambla, Barcelona's famous boulevard, and watch the street performers while enjoying some churros and chocolate.

Day 3:

Morning: Take a walk along the beach at Barceloneta and soak up the sun. Afternoon: Visit the Montjuic Hill and explore the Montjuic Castle and the Magic Fountain. Evening: Experience the vibrant nightlife in the Gracia neighborhood, known for its trendy bars and restaurants.

Day 4:

Morning: Take a day trip to Montserrat, a stunning mountain range with a monastery perched on top. Don't miss the breathtaking views and the Black Madonna statue. Afternoon: Return to Barcelona and visit the famous Boqueria Market for some fresh fruits, local delicacies, and souvenirs. Evening: End your trip with a sunset cruise along the Barcelona coastline, sipping on some sangria and taking in the beautiful views.

I hope this itinerary gives you a taste of the best that Barcelona has to offer. Enjoy your trip and don't forget to immerse yourself in the rich culture and history of this amazing city! ¡Buen viaje!