Hola! It's great to hear about your upcoming travel to Madrid, Venice, and Barcelona. Here are some useful travel tips for your trip.

Best Time to Visit:
The best time to visit these European cities is typically during spring (April to June) or fall (September to October), when the weather is most pleasant. Summer can often be crowded with tourists, but it's still a lively time to visit.

Route and Accessibility:
All three cities are well connected by Europe's extensive network of flights and high-speed trains. From Madrid, you can take a direct flight or a high-speed train (via Paris) to Venice. From Venice, you can take a flight or train to Barcelona. Cities also have efficient local transport like buses, trams, and metros for traveling within the city.

Accommodation and Booking:
Booking accommodation well in advance is advisable, especially during the high tourist season. Choose a location that is centrally located to reduce travel time within the city. All three cities offer hostels, budget hotels, and luxury accommodations, so consider your budget and preferences when choosing.

Clothing and Essentials:
Pack a combination of light and warm clothes as the temperature can vary. Comfortable walking shoes are a must as you will likely be walking a lot. Do not forget your sunscreen, a reusable water bottle, and a portable charger for your electronic devices.

Health and Safety:
European cities are relatively safe. However, do watch out for pickpockets in crowded tourist areas. Always keep your belongings secured. Also, make sure to have the right kind of travel insurance that covers medical emergencies.

Local Etiquette and Respect:
As with any international travel, respect for local culture and norms is essential. In Spain and Italy, tipping is not mandatory but is appreciated. Avoid loud conversations in public, respect dress codes at religious sites, and try to learn a few basic phrases in Spanish and Italian.