Go out the west gate, and then northwest from that large clearing that you get to when leaving the west gate. Keep following the northwest path until you see a fenced area with two spaces open on the top part of the road. Go up through there and you'll arrive in a forest. When you're in the forest, go up, then east, and then south to get on the path to the tower.
I would recommend Pendulum if you came for the NTR alone. It is fairly easy to get onto the NTR route by simply sleeping multiple times through one of the later scenes. If you go on the Hell route, you can't use the post-game settings to lock the characters into NTR or Love due to how Hell route works with the flags so it becomes harder to go for the individual one NTR, one Love routes.
A large portion of the missable scenes happen after you fight the dragon in Chapter 7. There is a guide for the basic scenes on the front page. There is also a sprite animation in one of the extended GoRs - lose to the Chapter 6 boss.
To see the sprite animation, you'll need to pick the first option when it asks you if you want to be able to see what's going on behind doors or if you want it blacked out.
