On Galaxy class vessels such as the Enterprise-D, the dilithium chamber/center of the warp core is located conveniently on the deck that matches the ground floor of main engineering. We can see on a few occasions how Starfleet personnel check or do something to the dilithium crystals by simply walking up to the warp core and extending a drawer with the crystals inside.
On the Sovereign class Enterprise-E, on the other hand, the dilithium chamber is located one deck above the ground level of main engineering, apparently quite far away from any of the walkways on the upper decks.
A schematic drawing of the same room can be found on Ex Astris Scientia.
How can maintenance staff access it in-universe?
Is there any extensible bridge or lift hidden somewhere (at least mentioned in behind-the-scenes notes, even if the actual set doesn't feature the mechanism), or do they actually have to bring a plain old portable ladder?