A detailed topo map on your wrist, plus winter and satellite
In WristTopo the map is the app, drawn by a renderer built for the Apple Watch. It packs in the detail you would expect from a paper topo sheet: contour lines, hillshade, trail names, alpine huts and viewpoints. Trails are drawn in the color of their real-world waymarks, so the red or blue blaze on the post matches the line on your wrist.
A tap switches the whole map to a winter style with ski trails, or to satellite imagery for rock, scree and pathless ground. All three work offline, and you can open the map any time, not only while following a route. Download whole areas and, if you leave the line to find water or scout a side trail, the terrain around you is still there.
Gaia GPS works the other way round. Its help center says that to see a map on the watch you first send a route from the iPhone, and that route brings a Gaia Topo map with it. It is a real topo map and it works offline, but it is the only map type on the watch, and it is tied to the route.