I had experienced such drops before. Three times, in fact, before that incident. The key was to breathe through the nose. It kept the food down and your nerves calm. On looking at Emmaline, I feel as if I should have informed her of such a technique, along with a few other precautions... 

Once we landed, I double checked the oximeter, making certain it read the air was breathable. It made little sense in my estimation on how the planet kept an atmosphere, but it read the environment was safe for humans. Even still, everyone had astra militarum-grade rebreathers on hand, and blessings of the God Emperor in the form of tokens emblazoned with the visage of Saint Lucia, Founder of the Order of the Valorous Heart. Mine was one of many emblams and fetishes of saints long past. 

The shuttle door opened like a falling anvil, hitting the ground with a resounding boom, cracking the very stone. 18 guardsmen and 32 PDF troops hustled out in rough skirmish formation, lasguns readied and scanning the bleak horizon. The ground was ubiquitous and uneven, as if the entire planet was the slope of a barren mountain. But the rocks were reddish black and almost burnt looking, and I loathed to touch anything on this forsaken planet. The air was breathable, but foul and tinged with dust. I took one breath and placed my rebreather on, if only to shield myself from the miasma. 

Emmaline, Lazarus, and I walked out of the shuttle. Fully encased in carapace armor and shotgun in my hands. I stepped past a PDF trooper, my keen eyes saw his arm visibly shaking. I placed a hand on his shoulder to calm him. I changed my optics from low-light to bio forms, and then to infrared, followed by ultraviolet. I cycled between them as my men began to spread out at my command, uplifting every stone and finding every corner in the landscape. Emmaline clutched the staff, obviously unwilling to make any attempt at using it until absolutely necessary, which was smart. 

Minutes later, I had a call from Lazarus. 

"Hadrian," I heard over the comm. I was in the midst of checking an indention in the rock, curious on if it was a footprint or an anomaly. If something had stepped here, it had to have been extremely dense. 

"What is it, Lazarus?" 

"I'm not archaeologist, but I calculate I have found the entrance." 

I had my doubts as I made my way a click to the north to reconvene with him, but once I stepped over the last rise, I realized Lazarus's remark was an understatement. I admit I caught my breath at the sight. There was a hole in the wall a cadre of Leman Russ tanks could roll through, only this hole was encased in a door of metal I couldn't recognize. Sinister lines of green pulsated slowly, as if they were the veins of some great, sleeping beast. To my horror, I realized the center plates of the massive gate were formed into a xeno skull the size of an imperial knight. From behind, Emmaline approached. I heard her intake of breath at the sight. 

"How do we open it?" She asked, breaking the somber mood. 

I pulled out the eldritch key and shook it in my hand.