Airport - the bus service is excellent and runs every 6 minutes to Placa Catalunya which is in the city centre. Costs ?4. To get back to the airport you just get the bus back again - there are always buses sitting at Placa Catalunya. Trip takes about 30 minutes. There is a locker facility at the airport to store luggage which costs ?4 per day which we made use of on the last day as we had been on a cruise and didn't want to carry out stuff about on our last day of holiday.
The metro is excellent. You can get everywhere so cheaply. Just works like London.
There are very few public toilets - none in the metro. Best place to go is McDonalds at the Placa Catalunya - otherwise you have to go into a bar or cafe and buy a bottle of water in order to use the toilet - I drink a LOT of water so it was a bit of a nightmare trying to find toilets but most of the main tourist places like Nou Camp and Sagrada Familia and Parc Guell have toilets.
The heat is stifling so make sure and drink enough or you'l get dehydrated and cystitis like I did. Thankfully there were literally pharmacys every hundred yards and I got tablets and was ok.
We went to Nou Camp, Parc Guell, Sagrada Familia, Parc della Cituadella (in which is the zoo) and the Ramblas. Be carefull of pickpockets (have a short handled shoulder bag) and also of overpriced food though we ate the first night on a streetside cafe on the Ramblas (just pizza and coke) for ?20 and the atmosphere was nice. Lovely ice cream and waffles on the Ramblas.Renting boat in the lake on Parc della Cituadella.

