Supergirl episode 15
Kara Danvers with James Olsen in Supergirl episode 15 promotional picturesCBS

Kara Danvers will head to Superman's Fortress of Solitude in the upcoming episode of Supergirl, which is aptly titled Solitude. CBS has released the synopsis and pictures for episode 15 airing this Monday (29 February) at 9pm EST.

The official synopsis reads as follows:

Kara travels to Superman's Fortress of Solitude in hopes of learning how to defeat Indigo (Laura Vandervoort), a dangerous being who can transport via the Internet and who has a connection to Kara's past. Also, James's relationship with Lucy reaches a crossroads.

Executive producer Andrew Kreisberg talked about building the fortress for Supergirl in an interview with Entertainment Weekly. Kreisberg shared: "Seeing the fortress is something I wanted to do since the beginning of the show."

"What's really fun about it is it's almost an amalgamation of every fortress that's ever been seen. There are bits of it that are right out of the comics, like the key to let you in, and we have Kelex, the Kryptonian robot in the tomb. Then there's other parts that echo the [Richard] Donner version as well, and there's other stuff that's brand new. That was really fun to be able to do," he added.

Melissa Benoist, who plays Supergirl, described the fortress as "magical" and praised the show's subtle inclusion of Superman. She said: "It's fun how we flirt with the idea of Superman being part of this world — how it is Kara's story, but they are still family."

"I love the way that they've included him in Kara's story with the messaging and things like that. This was the pinnacle of that. When we walked in and did that scene, it felt pretty epic," Benoist added.