From the Lost Realm rules:

At the beginning of each quest phase, if there are one or more side quests in the staging area, the first player may choose one to be the “current quest” until the end of the phase instead of the quest card that is currently active via the quest deck.

And from the Conflict at the Carrock Nightmare card:

Forced: At the end of the quest phase, if no progress was placed on the current quest this phase, place 1 progress on the current quest (bypassing the active location).

So, if a side quest was the current quest this phase

1) Do I place progress on the Conflict at the Carrock quest card, or the side quest?

2) Do I do so even if I placed progress on the side quest?

As written, it's pretty clear: the Conflict at the Carrock Nightmare card would place that progress on the current quest, and you get to choose what the current quest is. So yes, you could place progress on the side quest if (and ONLY if) you made no progress on it that turn.

However, the intent of that card was to put progress on the main quest, so that you can't simply stall on quest phase 1 forever. If the designers were to errata this card, I'm pretty sure they would change "current quest" to "main quest". For me, if I played CatC Nightmare and then used side quests to "stall out" the main quest by redirecting that forced progress token, I would feel like I was cheating and like I didn't really "earn" that win. So it's up to you: play the card as written (where you could place the forced progress on the side quest), or play the card the way the designers intended it, and the way they will probably errata it at some point (where you can't avoid that forced progress on the main quest).

The nihgtmare version is almost impossible (in solo) without side quests anyways, so it's better to stall for a bit.

Interestingly enough, I was hoping the progress would go to the main quest; I'm trying a strategy where I fish out the Battle side quest and try to keep it in play indefinitely so I don't have to do standard questing very much.

As written, it's pretty clear: the Conflict at the Carrock Nightmare card would place that progress on the current quest, and you get to choose what the current quest is. So yes, you could place progress on the side quest if (and ONLY if) you made no progress on it that turn.

It's not so clear to me, actually. The side quest is the current quest only until the end of the phase, after which it reverts to the main quest. When we're "at" the end of the phase, have we reached the end of the phase yet? It feels like an inflection point that could go either way.

You choose wich quest card will be active at the begining of the quest phase, so the quest you choose stays the active quest until the start opf the next quest phase.

You choose wich quest card will be active at the begining of the quest phase, so the quest you choose stays the active quest until the start opf the next quest phase.

Not quite correct. The rules say "the first player may choose one to be the “current quest” until the end of the phase ", emphasis mine. By the time you're in the Travel Phase, or the Combat Phase, the main quest has become the current quest again. I didn't realize this either until we started discussing it in this thread -- but unless Core Set Legolas is attacking during the Quest Phase , he's going to be putting his two progress tokens on the main quest, not on a side quest.

It's not so clear to me, actually. The side quest is the current quest only until the end of the phase, after which it reverts to the main quest. When we're "at" the end of the phase, have we reached the end of the phase yet? It feels like an inflection point that could go either way.

I think this is a case of two simultaneous effects, in which case the first player gets to choose which one to resolve first, and you could choose the resolution order that's most advantageous to you.

Did not interpret it right also! Thanks for the heads up... And it is logical that a side quest would be activated until the end of the quest... phase!

Is this similar to the Helm's Deep quest, or is the wording there different? I mean the part "if no progress has been placed…"

The Helm's Deep quest cards specifically say "on this stage" rather than "the current quest", so there's no ambiguity there. If you quested against a side quest, you didn't place any progress on the main quest, so you would trigger the effect.

Oh, yeah, sorry for a worthless question then. I should have checked the quest first, but I did not have the cards with me. Thanks for the answer anyway.