Two of the most famous buildings by Gaudí are literally a four blocks away from each other, Casa Milà also known as La Pedrera & Casa Batlló. Both are UNESCO Heritage sites so the entry price of a little over 21 Euros or $24 USD supports the maintenance and preservation of these landmarks.
Casa Milà (Metro: Diagonal) can be visited at night and you can even have dinner inside, which is may be a very touristy thing to do but it would also be a very unique experience.
Casa Batlló (Metro:Passeig de Gràcia) is a place I've dreamed about, although in my dream I could see the sea rather than gray rainy skies....
The entrance gives an enchanting glimpse of the whimsical lines in every room.
There are thoughtful surprises like a small skylight to add natural light to a dark corner
and doors designed with vents to naturally control room temperatures.
Even the ceiling has texture, and the glass designs above the doors and entries are different colors depending on which side you are facing.
and doors are unlike any you may have seen before
with views and shapes that invite you to smile:)
with a view of the back of the house
and the interior has a skylight and smaller windows on top to regulate lighting on each floor.
Tiles don't curve, so the corners are actually made of pieces made to look like they bend.
Some of the structures actually do bend, like the stairs to the roof
and the air vents on the top floor.
Mosaics make the chimneys works of art
and some portions reference the story of St. George and the Dragon
with small look out "windows" that face Sagrada Família (obstructed now by an apartment building).
Ecology was important not only in regulating the light and heat of the house, but water also. The roof has a room which collects rainwater!
It's great to have good dreams come true :)