Palmera is a small hostel (of the basic-place-to-sleep variety, not the party-in-the-common-room variety) one floor up from the street right behind boqueria market. My room had a single bed, a private balcony, a sink, kettle, a closet and safe, and came with cleaning/fresh towels each day. The reception is staffed 24h/day and you leave your room key with them when coming and going — seemed like a reasonably safe system, and the staff were nice. The shared bathroom was fine and I only waited for a shower once in 4 days. There’s not much noise from the street but you can hear everything going on at reception, so I recommend earplugs.
Overall, a solid option for a solo traveler who doesn’t want to do dorms.
Pro tip: don’t fear the 1€ coffee from reception, I avoided it until the last day because I assumed it would be bad, but it was actually perfectly tasty and nice to enjoy on my balcony.