you have to play all 3 stages in the expedition
now you can unlock veteran etc..you have always clear all 3 or you find one playing with you all 3 stages in a higher lvl
aslo yours are unlocked t...

How do I play 3 stages? After i kill final boss, the portal lead me back to city,I searched whole map but I couldn't find any entrance to next stage.

Weird, there should be a red "go deeper" portal and a white "return to town"
As well as a vendor shrine.
Try adding some difficulty to the expedition, one 2500 gold offering (roll area modifiers bar on the bottom during setup of expedition) should get you going.
Then delve all 3 maps and get good loot and productivity.
I am also not sure, but you may have to be level 43 to unlock veteran.

EDIT: I just saw on another post that you can click the bar itself when you enter a new difficulty.
You won't be able to activate levels until you do your first delve of 3 levels.
I think I had this issue and wound up adding one 2500 gold mod and dove 3 maps and got started.

Good luck!

Wen you activate Veteran button there's are small rectangles with levels below. Hit the higher value and start Expedition, when you finish 3 leves in a row (one after another without dying more than 3 times on each) you unlock next depths of Expedition.

There is no red portal, after I open the chest and show my result screen, only one go back portal show up.

Is it only available in online mode?

Open chest and get score?
Are you doing untainteds?
I don't think they progress level.

I see, so that is the case. Thanks for the info.