Build a Website - Specific but simple website needed.

I know that I am totally overly ambitious with this project I've taken on. But here's the deal. I want a website as part of a Christmas gift. I want to build my own Escape the Room game in my house for my partner to do on Christmas day. I will have puzzles and challenges throughout. As of right now, I have no site and no idea how to do this. But naturally, I'm trying to give the best gift possible in the coolest way possible. Here's how I need the website to work: I would like my site that work like this: on a page, a visitor would put in a code that I have given them by other means and by putting in the correct code, they would then be rewarded with a code phrase/word. For example: Page 1, the visitor must input the code word 'banana' to be rewarded with the code '12345'. Then, on page 2, which can only be accessed after putting in the correct code on page 1, they then input another code word and are rewarded with another code word- and so on and so forth. How is this possible? Or are there better ideas out there?