On this page of our guide to Wolfenstein: Youngblood you will find a detailed description of your first visit to the Catacombs. This is not a fully-fledged main story mission, although the return to the catacombs is obligatory in order to receive new main and side missions. During your stay in the catacombs, you may also take up optional activities.
When you visit the catacombs for the first time, after the Riverside mission, a cut-scene will launch. Three new major missions will appear in your journal:
Each of these missions is a difficult raid, i.e. a long expedition to an enemy base, in which sisters face a lot of exploration and battles with demanding bosses. All raids are initially marked with skull icons and this is a warning that your character is too low in experience to deal with mission objectives (too strong enemies etc.). First, take care of side quests to advance to higher levels of experience, as well as unlock new abilities and weapons.
Every time you return to catacombs you can find NPCs marked with exclamation marks. Each of these characters has a new side mission / quest. It's the best way to level up. Side quests involve visiting the main districts of Paris and offer some great rewards (like lots of XP, silver coins, and even free skill points). Side missions are described in a separate chapter of our guide.
One of the most important NPCs in catacombs is Abby Walker. You can receive a variety of challenges from her, which also can grant your some experience points and silver coins. We have discussed this topic further on the Daily and Weekly Challenges page of our guide.
In the catacombs there are many collectibles to find. As a reminder for taking each one of them you will get some XP. In addition, you can spend your free time playing Wolfenstein 3D on the slot machine in the bar - we described it more precisely on a separate page How to play Wolfenstein 3D?.
After you're ready to set out into the city, return to the subway map where you started exploring the hideout. When you interact with the map, the available destinations will be displayed. You can select the district you are interested in and the game will additionally display a list of tasks from the journal related to this location.
If you are having trouble finding out where to go to complete a specific mission or side quest, you can click on it in your journal. After the task becomes active on the subway map and when you reach a district, you will see the destination markers.
You can unlock next subway stations as you progress through the game. You can find more information on this subject on the Exploration and Collectibles page of our guide.