Introibo ad altare Deae

For several years I resisted having an altar in the house. I think I was reacting to so many beginners' books that tell you you have to buy the left ear of a saber tooth tiger captured on the third Sunday in September in a leap year, and under no circumstances haggle for it... Substitute whatever ridiculous example you like, you get my drift, that books are often over-prescriptive and make impossible demands.
That was why it was a relief to me when I discovered Phyllis Curott's book Witch Crafting, for while she does make suggestions for setting up Wiccan altars (she was initiated into the Minoan Sisterhood originally) she also has exercises for working without tools and without altars. She even called her tradition Ara (latin for altar) because the practitioners are the temples of divinity.

'During the same lunar cycle that you work without tools or aids [...], work without your usual altar. Take it down. Cleanse, bless and thank each of your tools, your symbols, your statues, your personal objects. Wrap them carefully and put them away.
'Try to work outdoors as much as possible during this cycle.
'As often as you can during the month without external forms, cast your circle and stand, sit, or lie at its centre. Ground and centre yourself. As you do, you will find the practice has more power, and meaning, than you have ever experienced before. Feel all of the elements within you - air in your breath, fire in your heart and belly, water in your veins, earth in your bones and all of your body. Revel in the clarity and perceptiveness of your mind, the passion that fuels your life, the love and all the emotions that flow through you, the strength of your body. Sing, dance, laugh, be silent. Pay attention to your feelings, for it is in your heart that you build a temple to the Divine. Feel the Sacred that resides within you, that is you, and that surrounds you.'
(Phyllis Curott: Witch Crafting, Thorsons, London, 2002, pp.237-8)

How much more does this example illustrate the freedom and ecstasy of the Goddess than slavishly following the instructions in a book and wondering whether you're getting it 'right'! However for witches the divine is not merely inside us, the reason we are encouraged to experience the elements within us is that our bodies are a microcosm of the macrocosm. All of the modern 'nature religions' 'pagan  traditions' and magical paths emphasise the immanent (divinity as within and tangible) over the transcendent (divinity as far away and intangible, requiring priests to contact for us), which is relatively more emphasised by the big three monotheistic religions. Therefore we experience the divine as external as well: this is a two-way traffic where we can both externalise our inner divinity and experience divinity as coming to us from external events, people, etc.
One of the ways in which the external divinity manifested to me was coming home one day to find a child's toy Mystery Machine (from Scooby Doo) on my front wall. I went out again and it was still there when I came home so I decided to treat it as a message from the universe, referencing one of my favourite TV programmes as a child and a lot of the things that that programme represented for me.
By this time I had an area set aside as an altar in the house. In fact the way witches use their altars means that they are not altars at all. Strictly speaking an altar is a place where sacrifice is offered. The Hebrew Bible describes the sacrifice in the temple being tied to the 'horns' of the altar to stop it getting away before it was sacrificed, and many Roman altars retain the remnants of incense offerings or have channels in the top to allow the blood to run away. This was one of the aspects of Roman religion that the early Christians 'baptised' by turning it into the final sacrifice of Jesus, which is re-membered in the eucharist.
Witches however downplay a sacrificial element in our way (except in so far as we consecrate things to divinity, or burn incense, or throw things into rivers, etc: sacrifice comes from two Latin words meaning 'make holy'), so that for most witches the altar is actually a shrine or else acts more like the altar in a Masonic lodge as a sort of combined bookstand, work table, and place for centring of attention.

A candle spell for a friend

In magic workings, as a priest of a chthonic Goddess, I tend to use the floor if I'm working indoors, even if upstairs. There is a crossroads near my house that was absolutely perfect for working at the dead of night (until the council improved the street lights), and I also often use a nearby tunnel under a road. These places have both been chosen for and by me, once again embodying the principle of two-way traffic.
My altar in the house, meanwhile, is very simple. I have a statue of my Goddess, which isn't always on the altar, because she likes her ancient symbols just as she likes nothing better than to be called by her ancient titles. She also likes things in threes, so at the moment it has a candlestick in the shape of a snake, a small soapstone dog, and a knife. This is not essential to my life and work, nor my connection with divinity, but is a place to remind me of the link, and functions in a very similar way to the picture of my father in the sitting room. I know we are all one and I have a connection to these beings, but there can be no harm from being reminded of it. 

A totally gratuitous picture of the high altar of Cardross Seminary: the most recent picture I could find online, i.e. showing the most damage to it. The early Roman Christians used the word 'Pagan' as an insult to mean the country bumpkins who stuck to the old religion after they converted to sophisticated city Christianity (none of these old religions survives in a continuous form today, by the way). Nowadays we would call them neds. The indentation on the top is where the stone containing relics of martyrs and other saints (which makes it the actual altar) would have been removed as the church was deconsecrated when the seminary closed. The state of this altar demonstrates an instance of triumphalist Roman Christianity in withdrawal and its place being taken over again by the pagans or neds!