https://organicmaps.app

Organic Maps is a free Android & iOS offline maps app for travelers, tourists, hikers, and cyclists based on top of crowd-sourced OpenStreetMap data. It is a privacy-focused, open-source fork of Maps.me app (previously known as MapsWithMe), maintained by the same people who created MapsWithMe in 2011.

Organic Maps is one of the only applications nowadays that supports 100% of features without an active Internet connection. Install Organic Maps, download maps, throw away your SIM card (by the way, your operator constantly tracks you), and go for a weeklong trip on a single battery charge without any byte sent to the network.