Learn Hardcore Russian: В аудитории в течение семинара обсуждались новые идеи. - During the seminar, new ideas were discussed in the auditorium.

The phrase в течение is a two-word preposition that always requires the Genitive case. It means “during” or “for the duration of.” That’s why семинар becomes семинара.

What case is аудитории, and why is it used with в?

Here аудитории is in the Prepositional case. When в indicates location (i.e. “in”), you use the Prepositional. So в аудитории means “in the auditorium.”

What does the suffix –сь do in обсуждались?

The suffix –сь can form two things:

A reflexive verb
An impersonal passive voice

In обсуждались, it marks an impersonal passive: “were discussed.” The thing being discussed (новые идеи) becomes the grammatical subject in the nominative.

Why are новые идеи in the nominative case instead of the accusative?

In the impersonal passive voice with –ся, the direct object of the active sentence turns into the subject of the passive sentence and takes the Nominative case. Hence “ideas” is новые идеи (Nom.), not Acc.

Can I change the word order, for example put новые идеи at the beginning?

Yes. Russian word order is flexible. You could say:
Новые идеи обсуждались в аудитории в течение семинара.
This just shifts the focus to what was discussed, rather than where and when.

Could I use были обсуждены instead of обсуждались?

Yes. That would be the perfect passive construction:

были (past plural of быть)
обсуждены (short passive participle)

были обсуждены emphasizes that the discussion was completed, while обсуждались (imperfect passive) highlights the ongoing process during the seminar.

What’s the difference between в течение and во время?

Both can translate as “during,” but:

в течение + Gen. stresses the entire duration (throughout the seminar).
во время + Gen. is more neutral, simply meaning “at some point during” or “during.”