It always is a bit embarrassing, while traveling, to walk into someone else’s important holiday … and know little or nothing about it.

A pre-Easter parade in San Blas, Mexico, in 2005. Bastille Day, which we didn’t see coming in Normandy three decades ago … and then tried to make amends by marching at the back of the Bayeux town parade.

And, today, getting caught up in the Festival of Saint John the Baptist — a major holiday here in Barcelona, Spain, where tens of thousands of dollars of fireworks are being blasted into the sky, completely unregulated, as we push into the wee hours of the next day.

We had hints, earlier, that something was up.

Starting around 3 p.m., individual “bangs” could be heard throughout the older part of the city, such as the Poble Sec district, where we are staying.

Predictably, sadly, the early explosions led some of us to think a bomb had gone off.

Well, it had, but it was not a terror bomb. It was local guys (and they have to be males, don’t they?) getting an early start on the fireworks.

A lot of people were flinching, as they heard the sharp report of an explosion, and many dogs cringed and whimpered, from the sudden noise.

The bangs continued into the late afternoon.

On our way to dinner, we encountered a couple of dozen women in traditional dress who were dancing as Caribbean drummers banged away, nearly blocking the whole of a pedestrian zone near where we are staying on a quick trip from France.

While eating dinner at a tapas bar on Carrer Blai we finally asked a food server what all the fireworks were about. Were they a regular thing?

“No, just today,” she said. “It’s Sant Joan’s Eve!”

“Sant Joan” is what the residents of Barcelona call John the Baptist, the first Christian martyr.

The festival also is pegged to an older, pagan holiday, celebrating the summer solstice. The typical first day of spring is June 21, but it has come down in history as observed on June 24, sometimes known as midsummer — when the ancients no longer had any doubts that days were getting shorter.

(See how it tracks with Christmas? The winter solstice is generally December 21, and Christmas is observed on December 25th.)

This is such a big event in Barcelona and Catalonia that some have suggested June 24 become the region’s “national” day.

The main aspect of all this, now, are the explosions going on into the night. It is like the city is being bombed by small but persistent aircraft. Drones, maybe.

As we walked along Carrer Blai about 10:30 p.m., more and more fireworks went off, often exploding quite close to pedestrians in the growing crowds at Carrer Blai. It was passing from “fun” into “irresponsibility”.

While stopping for Italian gelato, someone threw a big firecracker that landed about 15 feet from me, sending a lot of noise into my right ear, the good one!

It was turning dark and we accelerated our return to the apartment.

Hours later, explosions are still going off. Some are puny, those little balls kids throw on the ground, to create a sharp “crack”, and on up to the ear-splitting “bang” of a bigger firecracker going off nearby. Some even sound like the regular cough of a large-caliber weapon perhaps shooting at a plane or artillery gun — bang! … bang! … bang!

This apparently will go on all night, deep into Saint John’s feast day, which actually is June 24. (Fireworks the day before apparently is typical, but it does seem a bit odd that a city with a reputation for progressiveness allows the sale of potentially dangerous explosive devices.)

Religion is waning in Europe, but there is something about fireworks that incites kids to buy Roman candles and fire them off, whenever they get the chance. It seems as if every country needs a day when it can blow off fireworks.

Such as on holidays celebrated locally … but all but unknown internationally, and to the foreigners who just dropped in for a few days.