For the "Cuckold Investigation" quest, you need to use the magic ship to travel to Kirishima in the lower left corner of the beach and purchase the Alchemy Clairvoyance skill, which allows you to turn the wall in front of you semi-transparent.
Use this skill to see through the bedroom when the woman locks the door to trigger the cutscene and return to report.
As for the locked room in the dungeon of the prostitution organization, you can return to it after completing the process by obtaining the heart-shaped key in the quicksand area of the desert. When you rest at the Royal Hotel again, there's a button in the passageway that you can click to re-enter.
(However, the trigger in the Royal Hotel is severely buggy and prone to errors, so be careful.)
If you can't figure out how to enter the large room with a stone door deep inside while progressing through the quest, you can use the wall next to the small battle room.
In the Vampire Castle near the Ghost Forest, remember to get the wooden stake in the hidden room. After defeating the boss, use the stake to defeat it and then open the chest to obtain the Magic Stone. Otherwise, attempting to open the chest after defeating it will result in another fight. (Although the boss's stats are quite disappointing.)
When rescuing a hostage, a hostage will attack the protagonist's team. In that room, there's a hidden wall that leads to the next door to get the wooden stake. Beyond the fork in the road leading to the castle is a forest that connects vertically, horizontally, and horizontally. It's recommended to use the Wizard's Eye to navigate the map and navigate hidden paths to find the correct route.
Deep within, there are multiple rounds of battles involving numerous zombies. The final boss is immune to magic, so it's recommended to prepare holy-attribute equipment like a Demon-Breaking Dagger for a quick kill. Each round, the boss will use dimensional magic to send a teammate to another world, so quick action is crucial.
Afterwards, your teammates will return, and you can exit the forest normally. The two female adventurers rescued during the process will be rewarded with a magic stone as a token of gratitude.
Currently, the main storyline is plagued by numerous crashes, as well as some trigger issues.