yes, Changi is worth a look-see, and to keep you away from the bar for a bit..
did a circumnav of Changi terminals 2 weeks ago. Hardly comprehensive, but from the SQ J/F lounge complex in T3, turn L on exit, stay on upper level, don’t go down the escalator, and you’ll walk past the SQ gold and other lounges and you’ll find your way to the butterfly enclosure (2 floors) thereafter down to the main level. There are a bunch of food and drink outlets upstairs (and down,) but you will hv had plenty on the first flt, in the lounge and there’s more to come on the next flt, so enjoy the exercise..
find your way to the skytrain to T2, stay on the R side of the train to observe the fluid power of the Jewel’s waterworks. You can’t get off, you’re airside..
Continue on, and get off at T2, look over the orchid displays and thereafter find the escalator along and to the R, up to the SQ lounge. Show yr BP, gain entry, refresh as required because you’ll have a long-ish walk hereafter. First to the skytrain from T2 across to T3 (you can see the seperate SQ F landslide check-in terminal, first part of the massive T3 building:, with Crowne Plaza and Jewel further back) - and then a bit of a schlepp from the air train to the escalator back up to the SK lounge to complete the circuit. Nicest if you are returning to TPR, nobody will question your entry because they Know, But that’s for another trip...
Get yrself well-stretched, limber and hydrated prior, switch yrself to NY time (eat and sleep accordingly) and perhaps report back on yr experiences of 18 hrs?