"Loch Lomond" is a traditional folk song from Scotland. It is so well-known and ubiquitous that it could be called an alternative National Anthem. It is frequently sung at national sporting events, and you might also hear it sung towards the end of social gatherings involving music and dance (such as weddings and ceilidhs). The song uses a traditional melody and is essentially a tragic love song. There's no doubt that Loch Lomond is a romantic location. It is the largest loch in Scotland by surface area and very picturesque due in part to its many islands. The song as we know it originated in the Jacobite times, with "taking the high road" implying alive and "taking the low road" meaning dead. However the lyrics are easily interpreted simply as lovers who break up or part due to circumstances. The song was adopted as an anthem by the band Runrig, who performed it towards the end of their concerts. Unless the song is performed by live musicians, it is Runrig's rendition that you are most likely to hear at sporting and social gatherings.
There is an Irish song called "Red is the Rose" which uses the same traditional Scottish melody.
On mfiles we have two versions of Loch Lomond. This page is the version for solo piano, and you will find links for sheet music and audio in the left-hand menu or below. The other version on mfiles is for solo instrument with piano accompaniment, where there are parts for multiple solo instruments including Voice (with lyrics for 2 verses and chorus), Oboe, Clarinet, Bassoon, Viola and French Horn, though in many cases other instruments can also use these parts.
Here is a video of Loch Lomond for piano:
The image below is the first page of the sheet music, and here you can download the full sheet music for Loch Lomond for piano in PDF format.