The Secret Pedrera, Barcelona

I love Señor Gaudi's La Pedrera in Barcelona. It's really the roof I like, with its chimneys in the shapes of jousting knights and water tanks as swirling masses of fractured ceramics and the floor undulates like a wave crashing on the shores of Barcelona. It's a magical space that I return to every time I go to Barcelona and I never get tired of it.

The last time I went we queued for over an hour (refreshed by an ice cream) to get into the building.  I paid little attention to the trip through the show flat that demonstrates what the flats in the building looked like when the building first opened, or the displays in the attic - I headed straight for the roof to exult in the majesty of the knights, clambering up and down the floor to visit my favourite knights and take the same photos again and again. Some things are important.

I've only ever visited La Pedrera in the daytime, almost always the afternoon to enjoy the blue on blue skies over the building and looking over to La Sagrada Familia, the massive cathedral designed by Sr Gaudi and still being built. But, what would it be like at night? And that's just what the new tour allows you to see - the Secret Pedrera. Tours are hourly in different languages, small groups of about 20 people and a guide. Naturally, I had to go.

Our tour started at 9:15pm and began in the large courtyard with the guide telling us about the building and projections of the building shown on the floor of the courtyard before we headed up the stairs to the show-flat on the fourth floor which is furnished like it would have been back in the day. The flats are all quite large with rooms flowing into each other, some designed to be opened up to create larger rooms for parties and such. They're all very organic with a lack of straight lines wherever possible. This was all very interesting, seeing the beds and couches, the kitchen, the maid's room and uniform, the children's toys and bedroom and all that. But I wanted the roof.

Then up another flight of stairs to the attic and the displays of the building. The most interesting thing about the attic is the brickwork in the shape of a giant skeleton - I think the guide referred to a whale but I prefer to think of a dragon's skeleton and ribcage as the model for the attic. Sr Gaudi liked dragons and depicts them in many of his amazing works. The attic undulates and twists with brick arches drawing you in and the space is used to show objects and models of the building to help to explain its design and construction. I've been round the attic displays on each visit - that's how you get to the roof, after all - but it wasn't the attic I wanted to see. I wanted the roof.

At last I was let off the leash as we were invited to climb the spiral stairs to the roof and I didn't need to be asked twice. I was first to reach the roof and marvel at the knights lit by spotlights and glowing  under the starlight.

It was a magical sight to behold. The knights all a-glow with their magic and the ceramic coatings of the water towers shining in the spotlights. It was night, of course, so we had to be careful on the steps up and down the undulating floor of the roof but that distraction was a small price to pay for the vision in front of us. I immediately started snapping photos, most of which were out of focus but who cares? The guide told us about the construction of the roof but I was focused on the sights ahead of me.

After a wander round the roof we sat on the steps to watch a short show projected onto the side of one of the Big Lads - the water-tower at the corner of the building looking out towards Sagrada. That's the busiest with everyone wanting their photo taken there in day-time. The projection showed images of other Gaudi works, of the natural and organic elements that influenced Gaudi, of the sea and streams and flowers and, at one point the smiling head of Sr Gaudi's friend (and everyone's friend), the water-dragon at Parc Guell. That was great fun and a bit of a thrill to see him slowly creeping onto the side of the tank.

And then it was all over and we got the lift to the ground floor (I'd had enough stairs for the evening) and a glass of cava and nibbles before leaving. I toasted the bust of Sr Gaudi in thanks for yet more magic in that marvellous building. The guide mentioned that three of the flats are occupied but, when they're emptied, the building will become a museum and gallery to Gaudi.

The Secret Pedrera has opened my eyes to another side of the building. I shall go back again. And again.

Thank you, Señor Gaudi!