How to stop camera going through landscape whilst editing

How can I stop the camera going through the landscape mesh during editing - I cant seem to get as close as possible to the surface to view the position of something, or to ensure for instance up close there is no gap beneath a wall and the ground, without it taking many attempts and keep slipping through the nmesh. Or am I going about this the wrong way, maybe there is a snap to surface?

“End” key snaps vertically. You can also reduce camera speed for better control.