Help with location selection mechanic

what happens after you find the boss? Can I win the game my first turn by guessing the right room and defeating the boss?

Firstly, welcome to BGDF Shpee.

Idea 1
A possible mechanic would be to put an Event card or token on each room. Before the game starts, if you have 20 rooms you would deal 19 Event cards from the deck plus the Boss card, shuffle them together, and then deal them out onto the rooms. When you search the room, flip the card. The downside of this mechanic is cluttering up the board. The upside is that you could have other interesting events in addition to the Boss battle. It could be interesting if the event cards were mostly good and you had the choice of playing it or putting it back without showing the other players. This would let you weigh the benefits of bluffing vs taking the goodies, and also let you choose when to attack the Boss (assuming that you're not powerful enough to win if you attacked it on your first turn).

Idea 2
If you have a relatively small number of rooms, another option would be to collect tokens indicating which room the Boss is NOT in. Say you have rooms numbered 1 through 10, and there are 5 1-tokens, 5 2-tokens, etc. Before play starts, randomly select one set of 5 (without looking at it) and put them out of play, then put all the other tokens into a bag. Every time you explore a room, you collect a token from the bag. Once you have 9 different tokens you can move to the Boss room (i.e. the only token you don't have) and trigger the Boss fight. The downside of this mechanic would be that it could take a LONG time to collect 9 unique tokens, unless you have a trading mechanic whereby the players can "trade evidence" with each other (and/or "steal evidence"). The upside of this mechanic is that nobody can accidentally stumble onto the Boss right at the start of the game, since the Boss is only triggered once the player can prove which room the Boss is in.

Idea 3
Using the same tokens from Idea 2 but in a different way, the tokens could represent the threat level in the room. At the start of the game, put all the tokens in the bag. Players collect tokens by exploring rooms (or by some other mechanism; it doesn't matter). Each turn you must reveal one token. The tokens stay revealed. When any player enters a room, the threat level of that room is equal to the number of revealed tokens around the table. Once the threat level on a room reaches 5, the Boss attacks the next person to enter that room. The upside of this mechanic is that the difficulty of random encounters/traps could be modified by the threat level of the room, so the dungeon naturally gets harder as the game progresses.

Regards,
kos

Just some out of the box thinking here but. What if the monster/Boss was only revealed under blacklight (which you would provide). You might have some more options for hiding him and it would make your game really unique.