So yea ive found this out the other day and pretty much got it all down. to find this location, when you start off on the free explore, just go left and keep going through all teh tunnels and such and youll eventually make it to Skywatch. enjoy the grind my friends.
Also, slightly less reliably, you can do assassination quests, which give spin metal as a reward. It helps you reach 40 fast, which you can trade in for 250 glimmer and some crucible or Vanguard rep and marks., depending on who you turn it in to. Not quite as effective for getting glimmer, but you get the other perks too.