Upon further examination I don't think this is a secret entrance but rather that there wasn't room for the XXXIII label to fit in the crowded sketch of the room's contents, so the label is instead placed in a bubble pointing to the room. Idk it looked like a stairway to me for some reason!

Absolutely

I feel like you should be able to train in the weight room to become magically strong temporarily

That concludes my readthrough of B1: In Search of the Unknown! I hope you've enjoyed it as much as I have. This is a great introduction to any game of D&D - as good now as it was when first published. If you don't want to read the whole thread, keep an eye on my blog - I just might write a summary.

The Background Sheet also has a great list of tips for players:

The Players' Background Sheet reiterates much of the information we already know about the module's story, but adds this bit of detail which clarifies how the player characters know the location of Quasqueton:

There are some GREAT names here. Eggo of the Holy Brotherhood. Glendor the Fourth. Trebbelos, Boy Magician. Harg of the City Afar. This is Dumb D&D at its finest. There's an implied Great Church AND a Secret Church

You can also roll dice to determine what arms, armor, & spells NPC party members have. Players don't use these tables, but I see no reason why you couldn't do so if you wanted to use them for quick character generation. NPC party members can be as high as 3rd level & might start with magic items!

There's a neat little bit explaining how many henchmen are available (based on the number of player characters), what class they are (based on a die roll), whether they're secretly CHAOTIC EVIL (10% chance), & their personality traits (attitude, disposition, courage, & loyalty).

Next is a list of pregenerated characters, which can be chosen by the players (in lieu of creating their own characters) or recruited as henchmen. Players are intended to reference the Players' Background Sheet, which only includes name, race, & class. They don't know the characters' ability scores!

This is still the bare minimum number of monsters & treasure, so it is a pretty sparsely stocked dungeon, but I do think there's enough variety here to keep it interesting!

I also ended up with 14 treasures, which is one short of the 15 to 25 recommended by the module. To Area XXI (meeting room) I'll add a small wooden box containing 35 g.p. Tips collected by whoever the last guest speaker was?

-Area L (water pit cave): 1 bandit (friendly). Just fell into the pool & wants help getting the spear. Maybe it's their spear!
-Area LIII (the bat cave): 1 zombie (friendly) with 820 s.p. A former adventurer with a big ol' coin purse. Recognizes fellow adventurers & wants to join them!

I'm adding:
-Area XXIX (Erig's chamber): 4 skeletons (indifferent). Former guards awaiting their captain's return.
-Area XXXV (guest chambers): 7 goblins (friendly). Trying to open the false door & want help.
-Area XXXIV (false stairs/pit trap): 5 hobgoblins (unfriendly). Lost in the maze of doors.

I ended up with 11 rooms out of 56 which contain monsters. That's about 20%, which is a bit sparse considering I was using a 2-in-6 chance when stocking. It's also short of the module's recommended 16 to 20 (which is more consistent with 2-in-6). Let's go back & add 5 more to some random rooms.

Now that we've finished, let's see how I did with keying. Note that an "empty" room is not really empty, it's just a room that I did not stock with an additional monster or treasure per the module's instructions.

OH! This can explain why the troglodytes are trapped behind the web wall in Area XLII. NICE!

We conclude with Area LVI, which contains a statue which trollishly points towards a rocky outcropping of no significance. There's also a pit trap.

I also rolled up 2 hostile gnolls here. It would make sense to put them in the cave on the inner side of the secret exit, but I kind of like the idea of them being stranded on the ledge outside, ready to ambush anyone who emerges to steal their climbing gear.