How can I get this party started?

I'm trying to create a social/common area for my NPCs, so that they don't have to spend all their time hanging out in their bedrooms. Unfortunately, all my NPC housing to date has been apartment/hotel style and no one seems willing to leave their floor:

How should I instead construct my NPC housing so as to inspire them to mingle? I like the idea of having some kind of common room, but it's difficult to gather folks there if they're afraid of stairs.

Is there some way to get NPCs to travel up or down? (I'd prefer to avoid a sprawling, village-type layout.)

Update: Success! Based on Raven Dreamer's answer, I tried putting a single wood platform to split the difference between floors. Here's the merchant, having just bounced down:

Solution 1:

Bwarner has the right idea, but I have a different implementation.

The NPC pathing is pretty simple - amble back and forth, opening doors in their way. In your apartment style base, this restricts them to the same level as their "house", since they will not pass through wood panels, either by jumping up or by falling through (like you, the player is able to do).

What you can do is create what are effectively "one-way passages" for NPCs (no need to bother with removing floor that they're standing on!). In principle, this is quite simple: just put a drop of sufficient height (3 blocks should do it, 2 might, but I'd have to check) to the side of their house with their door. The NPCs will wander about during the day, fall off the ledge, and mingle in the pit you've created rather than alone in their homes.

Since NPCs teleport home at night (only when you're a sufficient distance away, though) their safety is not in question (though you could build a mosh basement as well, I suppose, that would keep mobs out regardless), and better yet, you won't have to re-corral them into the congregation pen every time you visited your town.

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Solution 2:

Another option that does not require a special housing arrangement is to make use of the King and Queen statues. When these statues are activated via wiring they teleport a single male or female (respectively) NPC the statue's location. When activated repeatedly they cycle through all of the NPCs.

To make use of this simply place the statues in your desired 'Mosh-Spot', place a pressure plate directly next to the statues, wire them together and jump on the plate. A single female and male NPC will appear in front of the statue. You can now leave them to it: as they wander back and forth they will step on the plate several more times causing all of their NPC companions to join them soon enough.

This has the added advantage of being able to "Get This Party Started" whenever you choose.

I created my NPC hangout on a small platform high in the sky (all of my housing was airborne) - the NPCs would sometimes fall off but be rescued from death by someone stepping on the button and teleporting them back (usually :S).