Returnal is an incredibly mysterious game by its very concept. You have to face a strange phenomenon for which there is no explanation yet – and only you can figure it out.
One of the first secrets that you will meet is the House. Your hero is an astronaut lost on a very strange planet. Exploring the very first location (biome) of the game – Overgrown Ruins – you will find a house with a locked door. This door cannot be opened right away, but if you are persistent enough, the method still exists. And the reward is worth it.
Returnal is an impressively detailed roguelike with randomly generated worlds that you’ll have to explore (and survive) to complete. Each cycle of this endless progression is surrounded by mystery, and if you want to defeat the boss waiting for you at the end of each territory, then you will need to get upgrades and abilities. In the event of death, you will have to start all over from the beginning. But some items remain in your arsenal forever. The house key is one of the first such items.
How to find the key to the house
The house (and house key) are located in the first biome, Overgrown Ruins. The house is a strange location that you can enter in subsequent playthroughs to receive bonuses. But the first time you can’t open it.
Continue through the Overgrown Ruins and eventually you’ll find a randomly generated cul-de-sac with an alien structure that you need to climb up a ladder. Scanning it will unlock the House Key for you.
The place and time of its discovery is completely random, so just keep moving deeper into the Overgrown Ruins until you find a room with a treasure. The house key is a key item, and it stays with you even after death, so you can use it in future playthroughs.
Use the house key to open the door. The first entrance to the house will unlock the “Welcome Home” trophy. When you explore the house completely and appear outside, an Astronaut Figurine will appear nearby. This is a special artifact that is used to resurrect the player. Always keep an eye out for further appearances at home. Completing scenes in the house will give you additional rewards.
A source: gameranx.com