A woman at the front of the queue cools herself off with a black lace fan. Beside her, a man in a crisp white shirt and fedora peers up at a statue of Jesus on the cross.
"This is something we've both wanted to see for a long time," says Meera Andrews, who is visiting the city on holiday from Wellington, New Zealand. The couple had planned to attend the 9 o'clock mass, then realized regular services had been canceled for the memorial.
In a nearby apartment block, two shirtless men smoke on their balcony as they look down at the scene below. One floor above, an armed policeman stands watch.
The air is humid, the sky overcast, as the city comes together to grieve.
Spain's King Felipe VI and Queen Letizia were joined at the mass by Prime Minister Mariano Rajoy, Portuguese Prime Minister Antonio Costa, Catalan leaders and other officials, as well as members of the public.
Inside, a mix of locals and tourists fill the pews, many snapping photographs of the cathedral's vaulted ceilings and stained glass windows on their cellphones. Large swaths of seats in the back of the cathedral sit empty as the Archbishop of Barcelona, Cardinal Joan Josep Omella begins his homily.
The city's archbishop says those gathered are a "beautiful mosaic" of society, all united in a common goal: "peace, respect, fraternal coexistence, and love."
Among the congregants were Freda Taah, 31, and Mathew Asuo-Asabere, 33, tourists visiting from Sydney, Australia.
"We had already planned to come to the cathedral, because we're Christians," Taah says.
Barcelona is just one of a string of destinations the pair is visiting on a seven-week holiday that criss-crosses Europe. And while they say they want to make the most of their time here to see the sights, they also want to be respectful of the tragedy that struck this city.
"You could feel the unity, you could feel that people wanted to come together in defiance and move on," Taah said.
While people prayed for the victims of the attack, outside the cathedral, a long line of tourists hoping to tour the famous landmark began to snake down the street.
Annalotta Scheinin, 32, was waiting in the queue with her boyfriend; the couple were on a weekend getaway from Turku, Finland, where Scheinin works as a resident anesthesiologist. Back home on Friday, she was treating victims of another terror attack, which left two women dead.
"Somehow you get used to the idea that these attacks are coming more frequently now," Scheinin said.
As the mass ended and the congregation slowly trickled out, Henrique Sposito, 46, gingerly pushed his sleeping son down the steps in a stroller.
Sposito moved to Barcelona from Brazil just four months ago.
"We chose this city to raise our son," he says, explaining that the city's liberty, multicultural energy, and safety were what attracted him and his wife here.
Their extended family was visiting from Brazil on Thursday when the attacker struck.
They were walking on a street adjacent to Las Ramblas when a crowd of people started sprinting towards them. Sposito grabbed his elderly mother's arm and his son's stroller, and rushed into a nearby restaurant.
"People were running like it was a bullfight," he said.
Sposito, who lives two blocks away from the Sagrada Familia, had come to the nearby Placa de Gaudi park to play soccer with his son, but decided to go to the memorial instead. One-year-old Davi was resting his head on a Barcelona Football Club ball, fast asleep.
"Probably the security is going to be more vigilant for some time, but look at this, we are here today and saw a king. It's the first time I see a king," he laughs.
While the country's terror threat level hasn't been raised, the heightened security here is palpable. Nearby, police patrol the streets carrying assault rifles. Two men were pulled out of the crowd of tourists and searched.
Tensions are also running high in the city's Gothic Quarter, where people have set up several makeshift memorials for the victims along Las Ramblas. Impromptu waves of applause break out every few minutes as hundreds lay flowers, light candles, and leave mementos.
Chants of "Barca, Barca, Barca," ring out as a group of FC Barcelona fans huddled in a tight circle at Plaza Catalunya, where the attacker's deadly rampage began.
Many people have posted messages of solidarity, written on sticky notes tacked onto market stalls, and scrawled on the silver plane trees that shade the boulevard.
Rosa Barahona, 22, was sitting writing notes in meticulous handwriting, while her younger sister Lucia Darriba, 13, and mother Alicia Alvarez, 46, both holding roses, chatted on a bench.
Barahona read one of her messages aloud: "Barcelona is pure ... It loves its people ... Barcelona laughs and grows with them, disregarding their nationalities, all of us are their people ... Barcelona loves us."