As the premium services do not exist on the Nintendo Switch version, players gain access to Vorugo Dungeon by completing quests from Miara. Each quest completed in the series allows the user to venture into further levels of the dungeon. If the user attempts to complete the dungeon before all levels are unlocked, finishing the last available stage will show an "area clear" notice, but the Auto-Explore function will not unlock and Achievements will not yet be awarded.
Editor Note (@ImaginaMagica): I didn't start writing this section until I had completed Journey into Vorugo 2. Please help fill in if you have the Switch version! I remember what the rough goals were - they are listed in [Square Brackets]. Rewards are also approximate.
Journey into Vorugo 1
there have been reports of monsters found only in Vorugo forest appearing levels go explore level one and report what you find
[Complete stage 1 of Vorugo dungeon]
[Up to Stage 5 unlocked]
Journey into Vorugo 2
[Get a military job - Scholars or Knights]
[Up to Stage 10 unlocked]
Journey into Vorugo 3
You'll need special permission to explore further into Vorugo Forest. You'll need to complete at least one (star)7 dungeon and achieve the title of Dragoon to receive such authorization.
[On the objectives in the description]
[Medium Health Potion 5]
[I assume Up to Stage 15 unlocked]
Additional Editor Notes about Vorugo:
More levels of this quest could exist, but I have yet to find them. Dragoon is a lofty goal!
Miala refers to the military jobs as "Joining the Martial Arts Organization" which is a localization issue.