Now that you’ve passed through huge amounts of mine and lengthy (but interesting and important) story, you’ve finally reached the far side of Colony 6.... and you still can’t get in. This side of the Colony is walled off as well, leaving you with only a large slope and a single switchback to explore- though the upper part of the switchback includes a landing area with two more ships like those used by the refugees from the colony.
The entrance to the mine via the lift you used to get out is closed off to you- but if you really want back into the mine, you can still use the Landmark travel option to jump back and then enter through the Drainage Channel again. You shouldn’t need to, though, unless you simply didn’t do any exploring at all. Sadly, the mine is still rife with Mechon.
More importantly, there’s more stuff to do here. Yay stuff!
There are some new monsters here to fight or evade as suits your tastes, and a Water Ether Deposit sits near the top of the hill, just outside Colony 6. It’s guarded by a particularly vicious Hox and its friends, though, so have a care as you head up. There’s also a Heart-to-Heart waiting here, but you won’t be able to try it until Reyn and Dunban are happy-cloud Affinity with one another.
If you decide that you want Dunban as your tank- or for some reason want to replace Shulk or Sharla with him- this is a good place to try it out, as most of the monsters are strong enough to be harmful, but not enough to be a big risk. It’s your best chance to try a change like that and adjust to it, as well as explore the possibilities of his Arts and any other new Arts you’ve managed to pick up.
The very next area is going to be the Satorl Marsh- and it’s hideously dangerous at night, so try to head into it at the start of the morning. Or, you know, mess with the time of day like the game lets you do. It’s kind of forgiving like that.
You may also wish to hop back to Colony 9 and use the Ether Forge to make some Rank II and III Ether Gems for slotting into your equipment.
And, if you happen to still be missing anything off the Colony 6 Collectapaedia page, now’s your chance to finish that off. You may as well take the time, you’re not going to be coming back here for much for quite some time- with Colony 6 closed off like it is, there isn’t a terrible lot to do in this area.