If I could have a hidden room in my house, I would make it a cozy, multifunctional retreat. Here's how I would envision and decorate it:

### Purpose:
1. **Reading Nook**: A quiet place to escape with a good book.
2. **Meditation and Relaxation**: A serene space for mindfulness and unwinding.
3. **Creative Studio**: A spot for writing, drawing, or any other creative pursuits.

### Decor:
1. **Entrance**: The hidden room would be accessed through a secret door, perhaps disguised as a bookshelf or a panel in the wall. The mechanism could be a hidden latch or a book that, when pulled, opens the door.

2. **Lighting**: Soft, adjustable lighting would be key. I'd use a combination of warm, dimmable overhead lights and strategically placed lamps. Fairy lights or LED strips could add a magical touch.

3. **Seating**: A plush, oversized armchair or a chaise lounge would be perfect for reading. For meditation, a comfortable floor cushion or a small futon would be ideal. A small desk with an ergonomic chair would cater to creative work.

4. **Walls and Flooring**: The walls would be painted in calming, neutral tones like soft blues, greens, or warm grays. One wall could feature a mural or a large piece of art. The flooring would be hardwood or a soft, thick carpet, with a few area rugs for added comfort.

5. **Bookshelves and Storage**: Built-in bookshelves would line one wall, filled with my favorite books and decorative items. There would also be storage for art supplies, journals, and other creative tools.

6. **Plants**: A few indoor plants would bring life and freshness to the room. Low-maintenance options like succulents, ferns, or a small potted tree would be ideal.

7. **Soundproofing**: To ensure the room remains a true retreat, soundproofing the walls would be essential. This would keep outside noise at bay and create a peaceful environment.

8. **Personal Touches**: The room would be filled with personal items that inspire and comfort me—family photos, travel souvenirs, and pieces of art that I love.

This hidden room would be my sanctuary, a place where I could retreat from the world and immerse myself in relaxation, creativity, and personal growth.