Arcol uses Mapbox terrain by default, but you can import custom terrain as a 3D DWG. Note that the DWG must have contour lines to work properly.
To import custom terrain:
Open the project location menu. This menu opens by default when you create a new project, otherwise you can open it by going to main menu -> Project -> Location
On the first screen of the menu click the "Import custom terrain" button to open the DWG import menu.
Click the "Choose a file" button on the DWG import menu and select a .dwg file from the file browser. Close the DWG import menu.
You will see the contour lines appear on the map and the imported file name with an X beside it in the bottom ribbon. If you wish to remove the imported file you can click the X. When you are ready to go to the next screen click the "Next" button in the bottom right.
The next screen allows you to click and drag to position the contours within the site context bounds you set up on the previous screen. When you are happy with the contour position click the "Next" (if you checked the Regrid box) or "Save" to continue.
Context buildings are positioned on custom terrain automatically.