Loch Ness is probably the best-known Scottish loch, thanks to its famous resident - Nessie, the exceedingly friendly, though unfortunately extremely elusive, Loch Ness monster. You can find out all about her at two dedicated visitor centres in Drumnadrochit, take a boat trip on the loch to get a closer look, or scan the waves from the ruins of picture-postcard Castle Urquhart. Do say hello if you see her.
Castle Urquhart was blown up in 1692 to prevent it falling into Jacobite hands; what's left is a classic romantic ruin jutting out into the loch. Loch Ness is 23 miles long and very, very deep - there's plenty of room for a monster.