Young Adult Bible Study Ideas?

I've done some stuff with "the bible project." We normally watch a video on the book of the bible, then do an inductive bible study on a passage, and that's worked well.  (https://thebibleproject.com)

Also, we've done some versions of this one. http://www.letterstotheexiles.com

Or really dig into some theology--what do they want to discuss? life issues? usually I find making tailored to them material is better than the quick easy stuff you can find on the internet. but that's just my opinion. 

Our Young Adults group (more in the late-20s demographic) does a simplified lectio divina on the passage that was preached the previous Sunday. Basically we ask three questions:

1. What do you see? (Observations, questions, comments on items of interest from the sermon.)

2. What do you hear? (What might be things that the Spirit is particularly bringing to your attention, why might that be?)

3. What are you going to do next? (What's a concrete - or as close to concrete as possible - step you can take to begin to live into this passage more fully.)

We find that having the sermon beforehand helps get discussion going, and the open format allows for us to explore the passage/topics around it as we want. Also, it's been helpful to us because really anyone can facilitate that format as opposed to needing a leader who has to do lots of prep. But some of that could just be because of the dynamic of our group. :)

Firstly, I think it's great that you're even asking this question. 
I have already commented with a recommendation on the Network's Facebook post (https://www.facebook.com/CRCNetwork/posts/1434502846645348) as to where you can find some good video series.   I also think that the comments already made here previously are quite helpful as well.  However, just asking out of curiosity, in "organizing something for this age group", are there actually people from that 18-30ish age group participating in organizing this group or is it just "older" members from the church, outside of that "young adult" range?

For our graduate student group, we tend to rotate between a study based on a book (that people can read but don't have to) or on a book of the Bible. Both of those require a bit more preparation from the person leading in terms of getting good questions prepared. I'd be happy to pass on to you some of the materials we've used if you'd find that helpful.

We've also used Tim Keller's video series "The Reason for God" (2009, Zondervan), which worked fairly well. The videos are dialogue based with Tim having a conversation about some of the common objections to Christianity, like "Isn't the Bible a myth? What about other religions? What are Christians such hypocrites? and more. 

Several others I know have found the series "for the life of the world: http://www.letterstotheexiles.com/" to be a great resource working with college age folks and other young adults. If you're interested, I'd be happy to mail both video series (a set of DVDs) to you (or anyone else on this forum who is interested - I also have the whole Rob Bell Nooma series), as they no longer fit how we do studies and I'd be delighted if someone else would benefit from them.