The interview process was intense and exhausting. I applied for a fundamental sciences group. The interview process included a 1-hour seminar, interviews with 8 staff scientists and an HR representative, lunch with other staff members, and a tour of the lab I'd primarily be working in. The 1-hour seminar was open, and had several dozen in attendance. People seemed engaged, and most interested in how the techniques I use could be translated into their groups work also.
The individual interviews were about 30 minutes each. I met with an array of staff, ranging from newer staff (~2 years employed at LLNL), through senior staff and management (15+ years at LLNL). Most questions focused on how I could introduce my current expertise to their working group, or what my career goals were. Discussions were typically relaxed, but very detailed (typical for science). Everybody emphasized how the lab works with postdocs to develop and support my long-term career goals, and would provide intellectual flexibility to pursue various projects. This was so ingrained in the culture; it was really exciting and refreshing.
The HR representative was fantastic and beyond professional. She spent about 45 minutes with me, introducing me to the laboratory, and gave a thorough overview of the benefits packages. I walked away with a much better understanding of the packages compared to other national laboratories and companies, which was quite comforting.
It was an exhausting interview that lasted almost 9 hours, but was a very positive experience.