Three days is the sweet spot for Edinburgh. It's long enough to do the city properly, the Castle and the whole Royal Mile, Arthur's Seat, the museums, the New Town, and the Water of Leith, but short enough that you never feel like you're padding. The mistake most people make is treating it as a bucket list and criss-crossing the city between them. This itinerary plans by geography instead, so each day flows in one direction and almost everything is on foot.
This is the three days I'd walk. Day 1 is the Old Town and Edinburgh Castle, top to bottom. Day 2 crosses into the New Town for whisky, gardens, and a Calton Hill sunset. Day 3 goes green: Holyrood, the Arthur's Seat climb, and the Water of Leith out to Dean Village and the Botanics. You'll cover 6-9 km a day, with only a short bus hop on Day 3.
Two bookings matter: your Edinburgh Castle slot and your Real Mary King's Close tour, both of which sell out and both of which anchor Day 1. Everything else flexes around the weather. And it will change on you, so pack layers and a waterproof regardless of the forecast. That's exactly why a free indoor museum sits in the middle of each day.
Got less time? Our one-day Edinburgh itinerary covers the essentials in a single walk. Got more? The 5-day itinerary adds Leith, Portobello Beach, the zoo, and the modern-art galleries.