Day 1: Porto (Arrival Day)

• Day 1: Arrive in Porto at 3 PM, explore Ribeira district and Dom Luís I Bridge.

Day 2-3: Porto (2 full days)

• Day 2-3: Explore Porto’s key attractions, including Livraria Lello, Clérigos Tower, São Bento Railway Station, Bolsa Palace, Vila Nova de Gaia (port wine cellars), Douro River cruise, and Foz do Douro.

Day 4-7: Lisbon (4 full days)

• Day 4-7: Explore Lisbon’s neighborhoods (Alfama, Baixa), visit Belém, Jerónimos Monastery, Tower of Belém, and take a full day trip to Sintra.

Day 8-10: Seville (3 full days)

• Day 8-10: Explore Seville’s main attractions: Alcázar, Seville Cathedral, Plaza de España, Triana, María Luisa Park, and take a full day trip to Córdoba.

Day 11-12: Madrid (1 full day)

• Day 11-12: Revisit favorite spots in Madrid, such as the Royal Palace, Gran Vía, Retiro Park, Templo de Debod, Mercado de San Miguel, and Almudena Cathedral.

Day 13-16: Barcelona (4 full days, including Montserrat)

• Day 13: Travel to Barcelona, explore La Rambla and the Gothic Quarter.
• Day 14: Full day trip to Montserrat.
• Day 15-16: Explore Sagrada Familia, Park Güell, Casa Batlló, Montjuïc, Magic Fountain, and the beach.

Day 17: Barcelona (Departure Day)

• Day 17: Departure from Barcelona at 11:30 AM.

Summary:

• Porto: 2 full days
• Lisbon: 4 full days (including Sintra)
• Seville: 3 full days (including Córdoba)
• Madrid: 1 full day
• Barcelona: 4 full days (including Montserrat)

This itinerary maximizes your 15 full days, providing a balance between exploration and relaxation across all the cities while ensuring you can enjoy key day trips like Sintra, Córdoba, and Montserrat.