All downloaded maps go into your "Exports" folder, (C:)>> Feralheart>> Exports.
If that doesn't work you can place .fhm into your Terrains folder, (C:)>> Feralheart>> Media >>Terrains.
The map may be crashing because there might be too many objects which is causing a lot of lag. Try turning off your water reflection and turning down your view distance to 0. You can also try switching your rendering system. You can find these options by pressing ESC>> Options>> Video.