After some time, Loki went exploring.
He was sure there was a place to bathe in the Underworld, but he had been unable to find it. The network of tunnels in Sif's underground palace confused him, and he often found himself turned around or right back where he had started. He never told Sif how lost he got, sometimes wandering the tunnels for hours without finding an exit, but he suspected that she knew. She asked him arch questions over his supper—how he was finding the underworld, if he had discovered anything new while she had been attending to her duty. He always gave some appropriately cryptic answer, but he didn't think she was satisfied.
He had been washing himself from a stone basin in Sif's bedroom. She had informed him that they were working on clearing on space for a guest room—and by "they" he strongly suspected "she," for he had seen no servants—but until then, he was free to use her chambers. He would be sorry to give up the bed, which he had grown rather attached to. It was a shame that something so expertly carved was so rarely used.
While the basin was doing its job—he washed thoroughly enough that he was far from dirty—he was growing tired of acrobatics it was necessary to perform in order to get himself totally clean. The Underworld wasn't necessarily a dirty place, yet Loki felt compelled to wash each morning, as if removing some kind of grime. He also knew that there must have been a place to bathe, for he had seen Sif on more than one occasion with her hair still damp, and she certainly hadn't been washing in her own bedroom. Still, he refused to ask her. He would find it on his own.
He set off in search of it one morning, a bundle of fresh clothing and a cloth with which to dry himself tucked under his arm. When he reached a fork, he took the right passage, feeling as if he had thoroughly explored the left in his wanderings. He took several wrong turns but soon found himself in a tunnel he didn't think he recognized. It was, admittedly, difficult to tell. While Sif seemed able to tell each stalactite and stalagmite apart, Loki would have preferred if there had been some sort of proper signage directing him to the location.
Like every other chamber in the Underworld, the bathing chamber had no door. But Loki had grown so accustomed to the lack of doors that he simply strode in, placed his bundle a safe distance away from the water, and disrobed. The chamber was large enough to fit two pools, and after some inspection Loki determined that one was warm and the other was cold. While the cold hardly bothered him, he chose the warm pool. He lingered longer than he had to, doing some laps and taking the time to think.
The Underworld was not quite so terrible, and he was admittedly surprised by how little he thought of Asgard. Sif had shown him the way to her expansive library, and he spent most of his time there, learning things that the books in Asgard would never have taught him. There was also a special, locked case that Sif instructed him not to touch, which naturally excited his curiosity. However, when he had tried to open it, he had been wracked by disturbing hallucinations that had left him crippled and shaking on the floor until Sif found him there several hours later.
"I told you," she tutted, even as she helped him back to bed. "Those books contain information on every soul in the Underworld, and they are not yours to touch."
"Can you touch them?"
"Of course. But why should I want to?"
He was interested in the Underworld, with its mysterious passageways and books about souls, with the elusive ferryman who brought the souls to their final rest and the creature he sometimes heard howling and barking. He knew there were things that the books in Sif's library could not tell him, things he could only know about through observation, and while he wasn't necessarily afraid of meandering the Underworld by himself, he also had no wish of becoming one of the dead. He wished to observe them, not join them.
But most of all, he was interested in the Underworld's mistress.
She was stoic at times, sitting across the long table from him while he ate. He would often catch her watching him, and she responded to his snide remarks with some of her own. She hardly ever seemed bothered by him, no matter how he tried to unnerve her. It was, on the whole—
"Impressive."
Loki started and looked up from the pool. He had been staring into it absently, and he hadn't heard Sif approach. She stood in the doorway, clad in her usual black, her hair slightly wild around her face, and she wore a smirk that told Loki all he needed to know.
He returned her smirk with one of his own. "Yes," he drawled. "So I've heard it said." He drifted over to the side and stepped out of the pool, water sloshing onto the stone. He retrieved his cloth to dry himself, and although he had the peculiar feeling that she was watching him, when he turned to look, her back was to him.
"I confess I am surprised you found your way here so soon," she said, turning her head to speak over her shoulder. "You've been trying to find it for several days, haven't you?"
"So you've been trying to sneak up on me in the bath for several days, is that it? Really, Lady Sif, if you wished to see me naked, all you have to do is ask." He finished buckling on his armor and gathered up the bundle of old clothes and the wet cloth. She turned back around to face him, her eyes flicking up and down his frame before they settled back on his face.
"I have something to show you," she said. "We'll stop off at my room so you may leave your things."
She navigated the tunnels with ease, and though Loki tried to remember which turns they had taken, he had a feeling he wouldn't remember the next time he tried to return. Sif led him to the bank of the river, and then they turned and walked along it. He peeked inside and was surprised to see a face that was not his looking back at him. As he watched, a ghostly hand reached out of the water and the fingers flexed as if trying to grasp at him.
"Ah," Sif said, having turned to see what was keeping him. "Yes, do be careful of the souls. They tend to get a little…grabby, and as you're living, it would be fatal to be pulled in."
Loki stepped away from the water and kept closer behind Sif, who didn't turn again to see if he was following.
"Where are we going?"
"Just a bit farther."
Where she took him was a huge cavern. Across a lake that fed the river was a queue. One by one, people shuffled into a small boat, piloted by a ferryman that Loki thought it best not to look at directly. Directly in front of them, however, Sif prodded something with her boot that Loki originally thought was a large, oddly shaped rock formation. However, as soon as Sif nudged it, it moved. Loki stared as three pairs of enormous eyes opened, and three huge canine heads lifted from massive paws that could have killed him in one swipe. The six eyes blinked blearily at Sif, and then the beast let out a surprisingly puppy-like yip that was so thunderous in volume Loki thought he'd be knocked over with the force of it.
"This is Cerberus," she said with a smile, reaching up a hand to scratch the chin of one of the heads. "My guard dog."
Loki eyed the beast distastefully. He had never been one for dogs, and certainly not for dogs this size. It did, however, explain the barking. "What do you need a guard dog for?"
"You'd be quite surprised how many of the living attempt to sneak in and rescue dead loved ones."
"Is that so."
"I can't afford to stand guard all the time, and so Cerberus does my guarding for me. If a living person gets on the boat, he will know about it."
"And then what?"
"He either expels them or they fling themselves over into the river the boat is crossing, which is unfortunate for them. It's the river of Pain," she said, seeing his raised eyebrow.
"Ah."
"Would you care to meet Charon, the Ferryman?"
Loki eyed the mad, demonic-looking Ferryman as he poled through the river. "Perhaps another time."