Attraction in Ciutat Vella, Bacelona

Ciutat Vella is the oldest part of Barcelona and it is situated in the city center. You can arrive by train, subway(L1, L3, L6, L7) or regular bus(or Aerobus to the Airport) to Plaça Catalunya. The district is divided in four quarters, Barceloneta, La Ribera, Barri Gòtic and Raval.

La Ribera

Palau de la Música Catalana is an UNESCO World Heritage site since 1997, which is a masterpiece of Catalan's Modernist Architecture. It was the headquarters of the Orfeó Català, the oldest Catalan Choir. The most beautiful part is fine glass ceiling inside of the Modernist Cencert Hall. As said by the director, the joy of the color, the glass and the atmosphere - these make it special and impressive.
Guided Tour of Modernist Concert hall (and Lluís Millet Hall and the Chamber Music Hall when available) : Euro. 12/adult (20% discount for Barcelona Card holders)
Personally, I highly recommend to listen to symphonic music inside as well as enjoy the amazing architecture. However, it is worth to have a guided tour if your schedule is tight.

Basilica of Santa Maria del Mar at Plaça de Santa Maria is a Catalan Gothic architecture featured a sombre appearance but with beautiful interior. It is located near the Picasso Museum.

Picasso Museum, where you can understand the formative years of Pablo Ruiz Picasso. Please note that it is FREE on the first Sunday on each month (close at 8:00pm).
Entrance: adults: Euro 9/adult

Raval

La Rambla. Often the first landmark that people identify with the city. It is the central and the most famous boulevard which cuts through the heart of the city centre and is a vibrant and lively promenade filled with Barcelona action at its best and worst. It stretches from the harbor to La Plaça Catalunya running through the Ciutat Vella like a spine. Come here to see the street performers jump out at unsuspecting tourists, enjoy the flower and pet stalls, or just sit back and watch all of Barcelona walk by. During the day, La Rambla is packed with tourists, at night, the locals come out, as well as many prostitutes. There, you can find newspaper and book stands, birds, flowers, musicians, street-performing artists that all contribute to create a lively and unique atmosphere. If you happen to be here after Barca win, you're in for a treat! A few blocks south of its north end, you'll find La Boqueria, a very large, fresh air (but covered) market.

Cansaladeria i Formatgeria Josep's is a market with front-line stand featuring most of hams and meats a tourist needs.

Barceloneta

You can just walk down La Rambla until the monument to Columbus in Barceloneta or take subway (L4 yellow line stopping at Barceloneta).

Parc de la Ciutadella is a central park, which includes a zoo, a lake and several museums. The Catalan Parliament can be found in the center of the park.

Zoo-Barcelona - was famous for its albino gorilla "Snowflake" and there is a a science museum inside the zoo today.
Entry fee: Euro. 16/adult.

L'Aquarium is the second biggest aquarium in Europe and is located at the Port Vell leisure center, next to the IMAX cinema.
Entrance ticket :Euro 16/adult.

Olympic Port is a dining and entertainment place where you can find lots of restaurants, bars as well as casino.

Beach stretches from the tip of Barceloneta in Port Vell till Vila Olimpica and so on. The beach is just 10-15 minutes walk from Barceloneta, or a few minutes from Vila Olimpica/Ciutadela.

Useful links:
The official website of Palau de la Música Catalana - http://www.palaumusica.org/
The official website of Picasso Museum - http://w3.bcn.es/V66/Home/V66XMLHomeLinkPl/0,4589,417470534_417617303_3,00.html