The department store El Corte Ingles publishes a helpful (and free) street map for tourists. You can pick a copy at the store, or from most hotel front desks. They're also available at the tourism information offices (including one at each terminal at Barcelona El Prat Airport).
By public transport
The Barcelona Bus Turístic links all of the Barcelona tourist sites you could possibly want to visit. It has three routes (map provided as you board), including a northbound and a southbound line that leave from opposite sides of the Plaça de Catalunya. Each takes 1–2 hours. The hop-on/hop-off format lets you get-off risk-free at any interesting stop, see what interests you, then get back on any later bus at that or any other stop. One approach is stay on for an entire route, then continue while getting off at locations that interested you earlier. Buses are double-decked, with the open-air upper deck offering much better views...sunscreen essential in summer months, jackets in winter/early spring/late fall. As you first get on, you are offered earphones. Outlets near every seat let you choose among many languages and playback volumes. As you approach each significant location, you receive audio describing it. You can buy tickets at the bus stops and elsewhere (e.g., better hotels) valid for one day (€24) or two consecutive days (€31).
The metro can take you to many places. Stations are marked on most maps; every station has a detailed map of exits to the city. A one-journey ticket cost €2, so it's best to buy a multi-person 10-ride ticket for €9.80 for Zone 1 which includes most tourist areas (called a T-10) or a personal 50-ride monthly ticket for €37.70. These tickets are also valid on the buses, trams, FGC (Catalan Railway Network) and on the main Spanish Trains (RENFE). 1- to 5-day public transport tickets are available that allow unlimited travel on the metro and bus networks (€7.25 for one day (a T-DIA), €13.40 for two days, €29 for five days). These are an excellent value. Be sure to look after them well as bent or damaged cards will not be read by the ticket machines (such cards can be replaced at one of TMB's customer service centers). Metro operating hours are: Sunday and M-Th 5:00 to 24:00, Fri 5:00 to 2:00, Saturday 24 hr (continuous service from Saturday at 5:00 until Sunday at 24:00). Trains are fast, often coming in two minute intervals. Announcements are made only in Catalan, though signs and ticketing machines are generally trilingual in Catalan, Spanish and English.
Pay attention to the fact that to get from metro lines operated by TMB (1,2,3,4,5, 9/10 and 11) to the ones operated by FGC (6,7 and 8), or vice versa, you need to exit and then enter through a new pay-gate. In this case, if you had a one-journey ticket, you need to get a new one. If you used a multiple journey ticket (such as the popular 10 rides T-10 ticket -the one that locals use the most-) you won't be charged for a second time when changing lines (as long as you are within the stated travel time for a single journey). To be clear, you get 10 journeys on a T-10 ticket, and once a journey begins, you have a certain amount of time (stated on the card) where you can use the pay gates the TMB metro, the FGC metro (6/7/8), TMB bus, tram, and local RENFE lines up to once on each journey.
Unusual features are: all cars are air conditioned; there are large screens for video advertising between lanes (e.g. at Universitat).
The Barcelona Card features unlimited free travel on public transport and free admission and discounts at around 100 visitor attractions. The card is available for purchase for periods of between 2 and 5 days, costing €27,50 for a 2-day card and €45 for a 5-day card. But you will get an online discount of 10% if you are booking in advance. If you don't plan to see lots of museums every day, then it is cheaper to buy transport-only tickets (see above).
But there are many things that you will want to do in Barcelona that are not eligible for discounts. You can't use the Barcelona card on fun transport options like cable cars, funiculars (except to Montjuic), for example.
Tramvia Blau is an old tram (beginning of the 20th century) connecting Av. Tibidabo metro station and Funicular station at the foot of Tibidabo. Costs: €4.50 for a two-way trip.
Funicular connects the foot of Tibidabo with the view point. Costs: €9 for two-way trip.
Mattia46, . 50cc 125cc 150cc 200cc scooters for rent.
GoCar is a two-seater, 3 wheeled vehicle that runs with a 49cc size scooter engine. It is legally classified as a scooter to drive on the roads. The GoCars were created with the purpose of being rented to tourists as a different way to see a city.
Scooters for singles or couples are a great way to explore Barcelona at their own speed. If you are coming as a group you can get a personal tour of all the places you want to see.
Cooltra Motos Scooter rental. You can rent a moped for 1, 2, 3 days and up to 1 month. You can also take part in private or group tours.
BornBike Experience Tour, . Takes you to the heart of Barcelona's culture through these tours: The Gothic to Modernism Tour, Beach Bike Tour, Montjuïc Tour, Tapas Tour (from € 22). Also offers bike rentals from 6 €. Close to Métro station "Barceloneta" (L4), Marquesa nº1, +34 93 319 00 20 .
Bicing, . (Barcelona's bike-sharing program, started in March 2007) is good option for an environment-friendly in-city transport. Unfortunately, it is just for residents.
Barceloneta Bikes, . Close to the harbor and the beaches, this company has different kinds of bikes you can choose to rent.
Bicimetrobike, . Barcelona Sants Train Station. City bikes, mountain bikes. They provide maps.
Biking in Barcelona, . Backed by Biciclot, a cooperative that promotes the use of bicycles in Barcelona.
Budget Bikes. Quality Dutch bicycles on hire. Offers group reductions.
e-bikerent, . Electric bike rental from €7 to 20 per day.
Mattia46 bikes & motos hire, . Bikes and motors, 1 day (24h) on bike for €6.
Terra Diversions, . Big selection of city bikes, mountain bikes, hybrid bikes, road bikes and children bikes in different sizes.
Barcelona is a very 'walkable' city.
Parking around all major tourist destinations is expensive (€3/hour, €20-36/day) and the spaces are difficult to navigate, as there are several classes of public parking spaces, with complicated rules for each class. Barcelona is plagued with the same problems that plague other major European cities; massive traffic jams and extremely narrow streets in some areas, coupled with a very complicated road system. As such, driving yourself around is not recommended for tourists, especially those with no driving experience in large cities. Public transport will get you to all the major areas, and you should use that as your main mode of transport.
Having a driving map is essential - plan your route before you set off. Navigating with an average tourist map is frequently misleading: many streets are one-way; left turns are more rare than rights (and are unpredictable). As an example, Gran via de Les Corts Catalanes is technically two-way, but in one direction supports only minor traffic: after every crossroad you'll find the traffic light on the next crossroad turns red by the time you reach it.
Some free parking spots reported by travelers are:
Near Moll de Sant Bertran (which is south-west from Museu Maritim) - driving at B-10, exit to WTC and make a complete round at roundabout, heading to warehouses - and park next to its employees cars.
Somewhere near Guell Park.
Near Font Màgica, in Plaça Espanya.
Getting around by car makes sense if you plan to spend much more time driving outside the city borders than inside it - and ideally if you don't plan to park overnight at all. Otherwise, for purely in-city transportation, consider renting a scooter, or using public transportation instead.