This is
the discovery of the bodies of Robert Scott and the other men on his failed Antarctic expedition in 1912.
So far as I can see, nothing in the text is very cryptic, but here are some explanations anyway.
Down as low as anyone can go
Surrounded by nothing but ice and snow
This day marks when the captain was found
Lying inside his tent, on the ground
I guess "low" means "south", though of course it's mere convention that maps have south at the bottom and north at the top. They were very close to the south pole, and certainly surrounded by ice and snow. Everything else here is obvious.
When he went he was barely old
But that didn't matter - he just got too cold
His fate read by the children of the land
As was to a newspaper's command
Scott was born in 1868 and the expedition left a few days after his birthday in 1910, so he was 42 years old. I would call that "not old" rather than "barely old", myself. The rest is, again, pretty obvious.
With tens of monuments erected in Britain
A final thing by his side - inside was written
About his adventures, his good and bad luck
As well as his final will in this old, tattered book.
As Wikipedia puts it: "In the dozen years following the tragedy, more than 30 monuments and memorials were set up in Britain alone. These ranged from simple relics—e.g. Scott's sledging flag in Exeter Cathedral—to the foundation of the Scott Polar Research Institute at Cambridge. Many more were established in other parts of the world, including a statue sculpted by Scott's widow for his New Zealand base in Christchurch." I guess the "final thing" here is his diary. I'm not sure it exactly counts as his "final will", but the last entry just says "Last entry. For God's sake look after our people."
