Cachly provides the following map layers:
Apple Maps
Google Maps
Ordnance Survey (UK)
Open Street Map
Open Cycle Map
Thunder Forest Landscape
Thunder Forest Outdoors
ARC GIS Satellite
ARC GIS Topo
Cachly had offline map tile downloads available. But in our upcoming 2.0 version we will be releasing Open Street offline vector maps, which will allow you to download entire states and countries offline in very small file sizes. (WA State is only 58 MB)
Yes, you can navigate to a cache using offline maps.