It's dark between the worlds, and cold in the way of spring days that trick you into leaving the house without a jacket. Most times when I arrive somewhere takes my eyes a minute to adjust to having things to focus on but Muspellheim is a whole other matter. There's little to it that isn't brightness, and no matter how I brace for it, it still boils over me. At first I thought of it like walking out of an air-conditioned desert building into the 118F degree heat, and the way it makes you feel immediately as if your skin has toasted, but at one point it also brought back a very visceral memory of waking up to a house fire when I was a teenager and that stuck too. I tend to parse the astral in terms of memories that evoke specific feelings, rather than getting a lot of visuals.
Surt and Sinmora are fire jotnar in Norse mythology. Surt is named in both the Poetic and Prose Eddas, usually in the context of rolling up to Asgard at Ragnarok with the sons of Muspell and taking out Freyr, but he is one of the oldest beings in the nine worlds. Sinmara is named largely without reference to Surt except for a late addition, and so while there is both academic and personal gnosis-derived arguments that they are spouses, my experience says it is likely. On the NTP shrine to Surt, it is suggested that the two might be a single being:
"Some say that she is actually Surt in female form, and that if you meet them, only one will speak to you at a time because they are actually magically the same being. Others say that Surt split himself in two in order to birth the race of fire giants."
My experience of Surt and Sinmora is that they are rather like twins who happen to be husband and wife, and yet like a single intelligence that chooses to manifest itself in two forms. If you don't have any reason to look past the way they present themselves, it's certainly possible to treat them like two separate beings and be in no way offensive. If you find the more theoretical stuff headache-inducing, there's no reason you can't just think of them as husband and wife and leave it at that.
Dividing seems to be very common, both in mythology and in nature. (That's where life starts, after all, with cells dividing.) Without division, whether metaphorical or literal, it's very hard to comprehend yourself. The ability to step outside of your own head, a universe that is by definition focused on you, and see yourself as other people see you and put yourself in their position, is essential to development and emotional growth. A mirror is not a perfect reflection, but in the attempt to create a mirror or a portrait, to separate and capture a part of ourselves, is a way to know yourself better in relation to that reflection. Surt and Sinmora are one being and two at the same time, because understanding requires being able to see yourself, and completion requires being able to integrate what you've seen into your self-concept, and this is as true for elemental forces as it is for mortals.