The journey from Parapat to Berastagi takes about 4 hours, again, depending on traffic condition. The roads from Parapat to Berastagi are mostly one lane, and pretty narrow.
Along the journey, one can stop by at Simarjarunjung to have a cup of ginger tea, and fried bananas. With the slightly low temperature there, what's better than having a cup of hot ginger tea and fried bananas to warm you up, while enjoying the scenic garden view there.
During my visit, a cup of ginger tea plus a piece of fried banana costs IDR16,000. Pretty reasonable price considering it is a tourist spot.