Some parts of Delhi are best understood not by visiting a single monument but by walking the streets and letting the place reveal itself. Put the map away, slow down, and follow your feet.
Pro tip: it's not easy hopping between, say, Shahpur Jat and Chandni Chowk. So hire an Uber on its 8-hour rental option — somewhere around $20–30 — and use it to move between these neighbourhoods. Get off, walk around, and if one doesn't grab you, move on to the next, or break at a nearby landmark or restaurant. The car waits; you explore.
The medieval quarter around the Sufi shrine of Nizamuddin Auliya — tight lanes, kebab shops, attar sellers, and the sound of qawwali drifting out at dusk. Go on a Thursday evening for the music, dress modestly, and eat as you wander. Living history, not a museum.

Chandni Chowk (the walk)
Not the shopping this time — the walking. Beyond the main bazaar lie the back lanes: havelis, hidden temples, a working spice market, a Jain bird hospital, parathas fried where they've been fried for generations. Take a walking tour or a knowledgeable friend; the best of it is invisible from the main road.
A warren of narrow lanes wrapped around a 13th-century tomb-and-lake complex, now packed with boutiques, cafés, bars and galleries. Medieval ruins and rooftop cocktails in the same square — Delhi's most photogenic collision of old and new. Quiet by day, loud by night.
India's first open-air public art district — the austere walls of a 1940s government colony covered in large-scale murals by artists from around the world. A slow, free, sun-permitting wander; come for the street art, stay for the contrast of bold colour on sober bureaucratic stone.
An urban village turned design enclave — a maze of lanes where couture studios, sneaker shops, cafés and street art hide behind an ordinary, slightly ramshackle exterior. Easy to get lost in, which is the appeal. For the fashion-and-design curious.
As everything on my recommendations, this too is a list incomplete. There’s much more to discover depending on what you might be in the mood for.