A lot of people here seem to think that regions are the only way to hide code. But they're not the only way, nor even the best way. Here's a better way.
In VS, go to Tools Options Environment Import and Export Settings. Copy the path and filename in the Automatically save my settings to this file box. Then open that file for edit. (Not sure if you can do this in VS and still have it work right, but otherwise use some other XML editor.) If in VS, hit Control-K, Control-D to format the whole file so it's readable.
Find the KeyboardShortcuts section. Then find the UserShortcuts section within that. If you've customized your keyboard at all, you should see various lines starting with Shortcut or RemoveShortcut. (If you can't find these sections, go into Visual Studio, customize a keyboard setting, then open the .vssettings file back up and look again.)
In among the Shortcut/RemoveShortcut lines, paste these:
Shortcut Command=Edit.ToggleAllOutlining Scope=GlobalAlt+Right Arrow/Shortcut
Shortcut Command=Edit.ToggleOutliningExpansion Scope=GlobalAlt+Down Arrow/Shortcut
Shortcut Command=Edit.CollapsetoDefinitions Scope=GlobalAlt+Left Arrow/Shortcut
RemoveShortcut Command=View.Forward Scope=GlobalAlt+Right Arrow/RemoveShortcut
RemoveShortcut Command=Format.SpaceAcross Scope=VC Dialog EditorAlt+Right Arrow/RemoveShortcut
RemoveShortcut Command=Edit.CompleteWord Scope=Text EditorAlt+Right Arrow/RemoveShortcut
RemoveShortcut Command=View.NavigateForward Scope=WebBrowserAlt+Right Arrow/RemoveShortcut
RemoveShortcut Command=Format.SpaceAcross Scope=VC Dialog EditorAlt+Left Arrow/RemoveShortcut
RemoveShortcut Command=View.Backward Scope=GlobalAlt+Left Arrow/RemoveShortcut
RemoveShortcut Command=View.NavigateBackward Scope=WebBrowserAlt+Left Arrow/RemoveShortcut
RemoveShortcut Command=Format.SpaceDown Scope=VC Dialog EditorAlt+Down Arrow/RemoveShortcut
What does this do? It remaps some Alt+arrow keys. Alt-Left now does Collapse to Definitions; Alt-Down toggles the item you're on; Alt-Right toggles the whole file between completely expanded and completely collapsed.
So when you open up a code file and the code is sprawled everywhere, just hit Alt-Left and it collapses neat and tidy, but you can still see the members. On the member you want to work on, hit Alt-Down to open it. (Or just double-click on the [...], of course.) If your file contains several classes, use Alt-Right (you may have to hit it twice) to collapse everything, even the class definitions, so you can open just the class you want.
All the code hiding you could ever dream of, and you don't have to use regions for any of it.