Rare journeys
Outside of these stories, perhaps the era that gave us the deepest explorations of the TARDIS was the early '80s. Christopher H. Bidmead’s stories Logopolis and Castrovalva - which featured the Doctor's fourth regeneration and its immediate aftermath - introduced brand new rooms in the TARDIS that we had never seen before, such as the Cloister Room and the Zero Room.
This deeper look at the TARDIS became a key feature of the Fifth Doctor's era, as we regularly saw glimpses of the companions’ rooms. These glimpses were little reminders that the TARDIS isn’t just a place to travel in for these characters - it's also a home.
All of the glimpses and journeys into the TARDIS - big or small - stand out because they’re so incredibly rare. For many writers, producers, and showrunners, the TARDIS is only meant to be something that leads the main characters to new places and new adventures, rather than being the focus of the adventure itself.
Generally speaking, this is perhaps the best approach to take. The fact that we have seen so little of the TARDIS has helped to maintain its sense of mystique. Still, it’s always exciting when we do get to explore and venture deeper inside the spaceship.