Arc de Triomf
(The NKs could have saved the effort since nobody knows about theirs. I'm able to report it only because I stumbled across it in a footnote in a Wikipedia article about the French one.)
Anyhow, the Spanish have one too. It's not all that big, but I think it has a friendly, accessible feel lacking amid the bombast of the one in France.

The Arc de Triomf was built to serve as the grand entrance of the 1888 Universal Exposition. It was at this exposition that Barcelona introduced the modernisme architectural movement to the world.
About the upper four sides of the arch are friezes of a decidedly unmilitary nature.

They are said to represent the Reception, Reward, and Apotheosis of Industry, Agriculture, and Trade. That sure is what it looks like to me.
So one might assume the event celebrated by this arch is the triumph of the economy. But then, what's with the bats?

It turns out they're are devices from the coat of arms of Jaume I. In 1229, he conquered the Moors in Mallorca—a triumph of a different sort. So I guess this arch commemorates both the defeat of the Infidel by Christianity and the vanquishing of Planned Economies by Free Markets.
Makes more sense to me than the French one. Their arch celebrates French military victories, from the Napoleonic Wars all the way up to the... er... Napoleonic Wars. Those that they won, anyway.
The playfulness of modernisme Catalonian architecture shines through in the goofy domes with ribs, crowns, stars and arched windows. Horn-blowing angels nod to an older tradition, but art deco wings give them away.

They sort of say, "Just kidding."
In all, I think it's a fine monument, defining the north end of Passeig de Lluis Companys, a broad pedestrian way flanked by ornate lampposts and palm trees.

Now, turn 180 degrees. What do we see?

How could they?
Who issues building permits around here? Don't tell me the Mayor and the City Council and the Planning Commission didn't know about this monstrosity. I mean, why didn't they just put an oil refinery there and be done with it?
That governs least, governs best. That allows eyesores like this, governs not at all.