Go somewhere interesting to do it!
The last itme I was that high (actually 11,200 on 1013) was over central-ish Scotland. Could see Inverness, Edinburgh, Glasgow but unfortunately not much of the west due to cloud. Apart from being colder than my heating could cope with it was rather nice. Interestingly the aircraft stalled and generally operated just as it does at sea level although the max climb was down to around 3 to 400ft per minute.
Strangely my Mogas did n't immediately convert to vapour or my brain shutdown due to hypoxia. But great views and easy to get there using a bit of wave lift. Shame its so blooming cold! (about -26 that day!)