TARDIS laboratory

When Ace was new on board the TARDIS, she explored its interiors and found the TARDIS laboratory. She thought it was similar to Frankenstein's lab, but with better lights. Ace didn't tell the Seventh Doctor she found it, because she knew he'd lock it up to keep her from making Nitro-9. She couldn't always find the place afterwards. (PROSE: Echo)

The Third Doctor once recalled a time when he created a gas in the TARDIS lab which pacified a herd of rampaging volcano creatures. (COMIC: The Arkwood Experiments)