Well I have never heard of 'Topoquest' and since I was a bit bored I decided to go have a look. BUT. I can find almost nothing about such a site, other than a couple of very short history lessons (http://wiki.gis.com/wiki/index.php/TopoQuest)
I did find this tho - looks like it could be a good alternative> https://en-gb.topographic-map.com/

So a little more searching and I found a link for the 'Official Website' (https://www.bing.com/search?q=topoquest&qs=n&form=QBRE&sp=-1&pq=topoquest&sc=6-9&sk=&cvid=762BD18CA94A4D78A9C11F28B7317230&ghsh=0&ghacc=0&ghpl=) Clicking it get's this response: This page isn't working at the moment topoquest.com didn’t send any data. My best guess: The website is probably dead.

Thanks for the response. I've been using topoquest.com off and on for about 20 years now, especially since I began playing with train sims 5 years ago. It would be odd that the website has 'died' all of a sudden...at least now I know the problem isn't PC-related.

Also, the link you provided as an alternative isn't what I'm looking for. The maps I used on topoquest were very detailed and show rail lines, even abandoned trackage in some places.

I've been able to find another way to access these maps; dunno if this has replaced the topoquest website or not...just am happy to be able to access these maps again. Below is a link in case anyone else is interested:

https://ngmdb.usgs.gov/topoview/viewer/#4/40.01/-100.06

Hope it all work out for you. Happy Train Simming