VenomXNL

TL-DR: Shift+L is used for Hide/Unhide landscapes. I know i know, i'm resurrecting a very old thread, first off, sorry for that. BUT: I was having the same issue and have been searching like hell on google, So to help possible others whom might experance the same issue, i've decided to post it on this thread since this keeps returning as the first search result in google when searching for it while being a very experienced modder (Professional programmer but just don't release my mods since it's for own entertainment mostly (or to custom/specific), i didn't knew about the shortcut i apparently hit accidentally in The GECK. It's not visible in the menus like View either, but after searching quite a while i've found that the Geck 'manual' shows the short cut which resolves this problem: Shift+L is used to hide/unhide landscapes. So again, my apologies for for resurrecting the old thread but this seemed to be the most useful location (considering the google search results) to post an solution for others whom are searching for it.