Any good recommendations for hiking / trekking map?
(beside OTP)
OpenAndroMaps (.org) with their associated Elevate theme. These are offline downloadable OSM maps with elevation contours, and particular attention to hiking-relevant details, such as mountain ranges and ridges.
OAM maps work in apps that use MapsForge-compatible maps, and Locus Map (for Android) is a fine example. Locus also has their own offline maps, very similar to OAM. This example shows the latter, with effort-sensitive auto-routing on trails:
mapy,cz is my favourite - main problem is lack of a proper attribution of OSM as a source
Osmand is nice
Organic Maps is nice in some cases but hiking tracks and contour lines are missing, but sometimes it is sufficient