Countours in Basecamp (PC) on the belgium.img map - how?

From the I downloaded the file which contains Belgium.img and Belgium_contours.img. I copied them in my Garmin GPS and when I indicate on the device to show me the 2 maps, I see the topomap, inclusive the countours. Fine, great.

I did the same for my Win PC which resulted in an execution file OpenTopoMap-Belgium.exe. After installation I can choose in BaseCamp on my PC the ‘OpenTopoMap – Belgium’ which is beautifull but … nowhere countours? Is there any possibility to have also the contours visible on this great map. How?

On the webpage there is also a column ‘PC’ for downloads. What is that?