There are three types of people in the world. Those who can count, and those who can't.
At first I had just assumed that Yamato had built the place with his special "wood" jutsus, but it was mentioned that "Yamato" was a codename given to him recently for his new team. Of course it is possible that he has had that codename in the past, so he still may have built the place.
my best guess is that yamato works is the name of that place
it was obvious that tag wasn't actually refering to yamato working on spying...
Sig By Damon Max
I think it has to do something with the first hokage.. The first hokage was the first wood element user so he could maybe have builed that far before now, so thats why Tsunade choose that name because there could be a ANBU working for the First in that time and she just used the same name..
... You're Dead 2 Me Now ...
It means he used his wood Jutsu to made those pillars!
"What Happen If I Fail ?"
dude the tag could be just a company name used to build the pillars i mean yeah... and besides Yamoto isn't yamoto's real name anyway so it would really have no connection to him.
Okay bear with me, I know this is off the wall.
What if that cave is where Oro used to do some of his experiments. Once he found out that the 1st's DNA killed every test subject except for one (Yamato) then he put up the tag saying Yamato works?