Tarragona  is the first large seaside town south of Barcelona. The town also offers a number of historical sites including churches from several different periods and a well preserved Roman colosseum. The town itself has the usual Spanish assortment of plazas sprinkled with cafes and tapas bars. Tarragona is a good choice if you only have a day or two to get out of Barcelona, otherwise the beaches further south or the remoter seaside villages to the north of Barcelona offer a more unique experience.
On Google Earth fly to: 41 06'56.51"N, 1 14'58.54"E
Tarragona's main station, Tarragona, is on the main train line between Barcelona and Alicante, served by 'Euromed' and 'Alaris' trains, as well as regional trains. Talgo trains run as far as Montpellier in the north, and Lorca in the south. The 'Trenhotel' night train to Granada and the 'Estrella' night train to Madrid also call here. Note that it's best to buy train tickets a few days ahead during the high season to avoid getting stuck in one place. However, you always have the chance to take a stop-train, which is reasonable when coming from Barcelona, as it basically takes the same amount of time.
Tarragona is also close to the Camp de Tarragona AVE station, on the Madrid-Barcelona High Speed line. From Camp de Tarragona, high speed trains run to Zaragoza, Madrid, Sevilla, Malaga, Burgos, Vigo, Bilbao and San Sebastian, as well as the 'Trenhotel' night trains to Burgos, Vigo, A Coruña and Gijon. From the station, buses run regularly to Tarragona and to other towns in the Camp, and taxis are readily available.
Furthermore, Reus airport also serves the Tarragona region. Reus is mainly served by charter flights and Ryanair.
All of Tarragona's sites are within walking distance of the train station. Taxis and local trains can take you further.
There are not a lot of organized outdoor activities in Tarragona beyond strolling through the town, swimming at the beaches, and people watching in the plazas. One of the most beautiful parts of Tarragona is the old streets (Casc Antic), the ones near the cathedral, do not miss them.
There is a cultural agenda 
The Tarragona 'Ajuntament' ie Town Council publishes a fortnightly online 'what's on' guide called 'publics' which can be accessed via the ajuntament website.
There are many interesting shops along the Rambla Nova and in the streets around it, as well as in the old part of the city. A lot of typical Catalan stuff can be bought there.
Tarragona has a number of small bars, restaurants, and cafes serving the usual selection of tapas, bocadillos (sandwiches), and local seafood dishes. The best area to browse for tapas and full meals is from The Plaça de la Font along the Carrer Major up to the Cathedral, with Carrer Nau and the Plaça del Rei and Plaça del Fòrum particularly worthwhile.
The Serrallo neighbourhood near the fishing harbour has some excellent fish and seafood restaurants, which are particularly popular for Sunday lunch. There is a market hall just off the Rambla Nova in the middle of town where the basics of a good picnic can be bought cheaply.
The nicest place to spend an evening is in one of Tarragona's many plazas with a glass of beer and plate of tapas. At night if you want to have some drinks and dance you should go to "El Port" (the port), there are a lot of pubs and dance locals there.
The tourist office at Carrer Fortuny in the New Town and Carrer Major in the Casc Antic can point you to hotel rooms at any budget.
Be careful if you choose to visit the night clubs of the Puerto Deportivo alone, especially if you are a guy. Foreign visitors have been robbed there.