They felt it was the right time to commit and book a flight to Paris. They had no reason to go there and didn't even particularly want to go, plenty of other destinations were more appealing. Around that time Paris was hit by strikes and protests over changes to the retirement age. There was also violence in London over student protests.
They had to cut their stay at Susanna's apartment short by 3 days as their flight to Paris was for Mon 25th Oct. There was no reason to do any of this but all they knew was the time was right to leave Barcelona and Paris was showing itself as the next place to be.
They had a week or two to sort out accomodation and didn't anticipate it being so difficult and expensive to find an apartment in Paris. Eventually they had little option but to book themselves into an Ibis hotel in the 19th district, just on the outer edge of Paris city centre, for 7 nights. After that, who knows?
The intense energy of Barcelona - good in short doses - was starting to feel a bit much and remembering their previous visits to Paris, they thought it might have a cooler, more open energy that was right for them now.
Before they left Barcelona they took a walk to the Font Magica. They had fond memories of it from their first time in Barcelona but this time arriving around 9pm and looking over the city waiting for it to begin they discovered it was broken (more water blockages?).
They found themselves walking home late that night along Carrer de Paris.