Thanks all of you!
Unfortunately I don't have any tips. I got it as a present two years ago. It doesen't really fit in my collection as I have mainly Paphiopedilum and Amorphophallus.
I didn' expect it too bloom, therfore it was standing and not hanging, so the first spike got squeezed and brought only one flower. But two spikes were following while it was hanging.
It is indoors at a south facing window, in a basket with Sphagnum, it gets a shower once or twice a week. Temp is hot, never goes under 20°C in winter, in summer it has about 28 - 33°C with peaks of 37°C. Humidity has a range of 20%-50% in winter and 40%-80% in summer. In these conditions I don't have any idea why it is blooming...