What a shotengai is
A shotengai is a covered pedestrian shopping street, usually lined with a mix of small independent shops, restaurants and stalls that have often operated in the same spot for generations, sheltered from weather by a roof running the length of the arcade. They function as a kind of pre-mall neighbourhood commercial spine, still very much in daily use rather than preserved as a novelty.
Tenjinbashisuji: Japan's longest
Tenjinbashisuji, running south from Osaka Tenmangu Shrine in the Tenma district, is commonly cited as Japan's longest covered shopping arcade at close to three kilometres, split into several numbered sections. Walking its full length is less a single attraction than a slow cross-section of how Osaka actually shops and eats away from the tourist centre.
Why they're worth seeking out
Shotengai tend to have far fewer English signs and far fewer other tourists than districts like Dotonbori, and they're one of the more reliable ways to find a genuinely local lunch spot or a small specialist shop that's stayed in the same family for decades.