Here is the fix

1. Close the Viking application

2. Open file
   C:/Users/<\user name>/AppData/.viking/viking.ini.
   The path might be slightly different to that given above, I did it on a friends laptop and had to come back to it later, so am not 100% sure of the path, but the file name you want to change is definatley called viking.ini. Search for it in File Explorer and you will find it.

3. ... and add this line to the bottom of the file and save it
   curl_ssl_verifypeer=0

4. Open Viking again and opentopomap tiles should now load and be displayed
   If the map layer is not showing be sure to right click on the upper left hand panel and add a map layer. Make sure the map layer is opentopomap, which it should be by default, then you will see the maps loading.

I found the fix here
https://sourceforge.net/p/viking/bugs/149/#8687
which is a closed bug on Sourceforge, but the bug is clearly still there

Can we get a fix when time allows, please.

I suspect the real reason is that Viking uses libcurl which in turn accesses a certificate store to verify the HTTPS certificate against and this is failing - i.e. getting curl error: 60 for uri... messages in the message log.

AFAIK For Viking on Windows this certification store (I'm not even sure where this is - if there is even one - there could be some defaults built into the curl library itself) can only be generated at build time - and then is not updated any further. Thus these verification methods can have expiration dates and can start to fail - hence the above disabling of the verification gets the Tiles working again.

For background reference on certificates see here (especially the first part):
https://ubuntu.com/server/docs/security-certificates

For most versions of Linux - this is handled at a system level and are periodically updated - such that individual programs don't have to manage this certification update.
I assume for other Windows programs - e.g. web browsers - they update often (and have teams of people who can manage such things) and include updates to certification stores.

Viking on Windows has no such luxury or support. And further I think there is difference in binary format between Linux and Windows - such that I can't simply copy the latest file(s) from a Linux system and install them on Windows either.

I'll think about turning off the SSL verification in the Windows build - if that means the default (OpenTopoMap) Map service works by default.

Hi Rob
Thanks for the reply.
I suspect that most people are using Viking as a hiking app which makes OpenTopoMaps essential.
In other words without effective hiking maps folks will do a quick uninstall and move on.
I would simply turn off the https certification for OpenTopoMaps at compile time becasue it has to be turned off in any case to get Viking working on Windows as outlined in the fix above.
It will save a lot of hassle for bamboozled Windows users who are spending, in my case, 2 hours (wasted) trying to figure out what is wrong.
(I installed this on a friends Windows laptop but I use Linux myself where the Viking app works flawlessly)