I see this argument from time to time; you can either run a free form, sandbox game, or you can run modules. The implication is that to get your players into the module, there has to be a degree of railroading going on.
There is an approach that splits the middle. I think most of us do it already, I just don't know that it has a name. I'm calling it, The Sandbox of Modules.
Here's what you do - take your favorite map, take your stack of modules, and liberally sprinkle the site locations for the modules all over the map. Rename the locations as necessary; White Plume Mountain becomes Bright Doom Mountain, and so on. File off the plot hooks; chances are it's a tournament (railroad) module and the plot hooks sucked anyway. Generate new plot hooks, plant them in the setting, and wait for them to be discovered.
After 35 years of publishing, there is a metric crap load of modules out there, and lots of them are pretty good. OSR modules are available economically as PDFs. There is no reason you can't overwhelm your players with choice whenever they decide to do something else and go looking for adventure. Never railroad again!
Site-based locations are obviously best for this approach, so I'm always looking for new OSR site-based locations to go along with some of the best from the TSR and JG eras. You can put all the devilish and difficult modules in there right from the start; "No one goes into them there hills, seeing as the Hill Giant Chief has a well-known Steading out there. It's a bit too remote and barren for the Duke to send an army to clear them out, long as they stay on their side of the river..."
By keeping some notes in a binder, some on the computer, some behind the screen, my (adult) players never really know if it's homebrew or a module; once the train tracks that lead to the adventure site are planted in the world, part of the craftsmanship is camouflaging the train so it looks like a party-on-wheels, covering the tracks with dirt, and letting your players blow the whistle and stick their head out the window when they hit the open road. No one ever knows the difference.
Isn't this one of your guilty pleasures as a DM, to take your campaign map and slide your favorite modules in there, like easter eggs? (Ooh, I bet this remote place could be The Keep on the Borderlands).
You've already seen the Sterich map for Gothic Greyhawk; here's the Geoff map from the kid's game as a smaller scale example. The kids have spent most of their time exploring Stonehell up in West Town, but I've got B5 Horror on the Hill ready to go (Guido's Fort, of course!), Fort New Rock just west of Tika Town is The Keep on the Borderlands, and I planned on placing B3 The Palace of the Silver Princess down in the Hornwood (it is a kid's game, after all).