The canal and the signs
Dotonbori runs along a narrow canal just south of Namba station, and it's built almost entirely for spectacle: oversized 3D signage advertising crab restaurants, pufferfish lanterns and takoyaki stalls stacked above street level. The Glico sign — a running athlete in neon, refreshed through several generations since the 1930s — is the unofficial meeting point for the whole city.
It's genuinely busiest, and best, after dark, when the signage does the work daylight can't.
Namba, just behind it
Step back one street from the canal and you're in Namba proper — a denser grid of shopping arcades, department stores and the Nankai Namba train terminal, which is your gateway for day trips toward Kansai Airport, Wakayama and Koyasan. Namba Parks, a terraced shopping and green-space complex, is worth a look even if you're not there to shop.
Amerikamura, a short walk west
West of Dotonbori is Amerikamura ('America Village'), Osaka's youth fashion and streetwear district — vintage clothing stores, record shops and a noticeably younger, more subculture-driven crowd than the tourist-heavy canal itself.
Eating your way through it
This is the district most associated with Osaka's food identity — takoyaki stalls, standing-only okonomiyaki counters, and the Kuromon Ichiba Market a short walk east. Expect queues at the most famous storefronts and treat them as a starting point rather than the whole meal; some of the best food here is one street back from the main canal.
Dotonbori is at its most crowded on weekend evenings. If you want photos of the signs without a wall of people in front of them, an early weekday evening — after the lights come on but before the peak crowd — is the sweet spot.