One of 3 houses by Gaudí in Barcelona that can be toured.  truly amazing and worth the visit.  go in the mornings, before the site gets crowded with architecture students.  your admission price includes an audio guide that is informative, albeit a bit over the top "gaudi was surely one of the most inspirational artists of all time..."  located at Passeig de Gràcia / Provença (metro stop across street)  phone #  34 93 216 03 06

Actually there are 3 houses of Gaudi that can be toured. Casa Batlló, Casa Milá and Palau Güell. You don't have to stand in the queue if you buy online ticket, that can be saved on your mobile phone (not as an SMS message).  

Casa Batllo's website (in English)