Travel to Spain
As Spain is part of European mainland, it can be reached by air, rail, road or sea. For international travellers from places other than Europe, if Spain is the first port of call, it is very likely the arrival city will be Madrid or Barcelona. The Barajas airport in Madrid is one of the biggest in Europe. There are airports in some of the top tourist destinations but they are largely connected to few European towns, with seasonal flights to other locations. Depending on your itinerary, it would advisable to check if it is possible to arrive in say Madrid and depart from say Seville. Saves time journeying back to Madrid or Barcelona.
Travel within Spain
There are few low cost airlines operating internal flights. If travelling to an island, Air would be a better option. High speed trains are also very comfortable and quick. A distance of a little over 500 kms from Madrid to Seville is covered in 2 hours and 30 minutes to 3 hours. The minimum return fare varies from ~Euros 70 to ~140, depending on the class of travel, time of travel and if you book a bit ahead of time. Flexible fares cost more. Air travel by low cost carriers may actually turn out to be cheaper.
Driving a car too is fun, though it would take more time. Buses are the cheapest way to travel though long distances will not be comfortable.
Visa
Indian passport holders need to apply for Schengen visa. Takes 3-4 weeks.
Currency
It is Euros.
When to visit
Madrid – The city is an anytime of the year destination. July to August is the peak season and also a bit hotter, with temperatures topping 35 degrees celsius. Try to avoid this time. December and January can be a bit cold but it is mild unlike cities to the North and is a good time except perhaps around Christmas and new year when there is more crowd. February to May/Early June and September to November is probably the best time and the crowds will also be a bit less. I went in June and it was light until after 9PM!
Seville – Much hotter than Madrid, it is one of the hottest cities in Europe. Temperatures top 40 degrees Celsius in summer. Good to avoid peak summer time of July and August. February to June is the peak tourist season.
You can also plan to visit during some of the more important festivals, though there will be more crowd and prices of accommodation higher.
Accomodation
Madrid
City center, or Centro, which is an area of about ~5 sq. kms is a good place for a tourist. Plenty of options but for a good hotel with breakfast, budget a minimum of Euros 100 per night. The first time, I stayed near Retiro park and Atocha station and on Gran Via the second time, very close to a metro station.
Seville
The center of Seville is compact and walkable. With many attractions, it is probably the best place to stay for a tourist. Either Santa Cruz and Centro area. Do remember that if your hotel is in a narrow lane, taxis may not be able drive all the way. I was dropped a very short distance away and had no choice but to walk.
Again fair bit of choice for accommodation and it is bit cheaper than Madrid. Budget Euros 80-100 per night for good accommodation.
Vegetarian food
Spanish food is meat based even though there will generally be vegetarian dishes. Not always easy to explain vegetarian means no meat, chicken or fish(and no eggs for many). In Madrid and Seville, there is no problem as international cuisine, including Indian and American QSR, is available.
Meals are reasonably priced. In a QSR, budget can be ~Euros 10 per person. In a decent mid range restaurant, a meal for a couple can be had for under Euros 50.
What should be tried are Tapas(even vegetarian options are available), Churro( fried dough pastry), perhaps with coffee, and Sangria, a wine drink.
Language
Easily manageable with English.
How many days
Just Madrid and Seville, 3 days in each city should be adequate, unless you are planning day trips.