Planet is earth sized.  Fantasy medieval setting that takes place on Continent A, which is on the other side of the planet from Continent B - about as far as South America is from Asia.  Continent B has a very very tall giant lumbering around on it, so big that it basically wrecks the landscape of Continent B wherever it goes.  Presumably, at a certain height the giant would cause such enormous tremors that everyone everywhere on the planet would hear it walking around - I don't want this.  But I do want the giant to be as big as possible without being a nuisance to everyone else on the planet.  A global tremor when it jumps up and down would be okay, but there's already so much going on in this world I don't want the distraction of a constant background rumble from this giant just going about its everyday business.  How big can I get away with?

Update: don't worry about the structural integrity of the giant.  The giant is magic, but the planet's geology is not*.  Assume human-proportional mass for a given height. 

Update: I want the giant to be as large and (locally) devastating as possible without causing global devastation. "Local" devastation can be as great as rendering all of Continent B uninhabitable, but if this isn't possible without causing a few raised eyebrows on Continent A, then no dice. 

*except to the extent that all geology (and geologists!) is magical ;)