During the past 5 years, I spent time (2-4 days) whenever I was on a "Mileage Run" to a new city or a city that I haven't been to in a long time. Some of the more memorable routes/trips included;
LAX-BAH - $750 RT fares, for 19,000 miles. Took several trips. On a couple of trips, stopped over in Baharain and Kuwait.
SFO-HKG - In 2017, took 4 $1000 RT (W fares that I was able to upgrade). Took 2 RT for $600 RT. Usually spend a couple days in HKG.

Other "Mileage Run" trips (spent 2-3 days at site) with low fares included, PEK, HGH, TPE, PVG, HND, KUL, SYD, IST (*), MEX, BEY, SOF, DUB, MNL, ICN, CAI, NAP (**), LIS (**), FCO (**), CPH, CDG, LHR, VIE, LIM/CUZ (Machu Picchu). While I enjoyed all the trips, Machu Picchu has to be one the most memorable.

(*) In addition to visiting IST, on other trips took inexpresive Turkish Air to other cities (Antalya, Ankara, Kayseri).
(**) In 2014, United offered $1500 Business Class fares from SJC to Europe.

Domestic Mileage Runs. I was fortunate that many of the Domestic Mileage Runs, also coincided with my Business Travel. For the most part, I was opportunisitc and agnostic on the domestic Mileage runs. I would find most on Flyertalk Mileage Run. Some of the more memorable Mileage Runs where I booked/took several trips included;

SFO/IAH/PDX - 2014 this priced out <$200 RT, provided 7,000 miles.
SFO/DTW -. 2016/2017, this priced out <$200, provide 5,000 miles.
SFO/FLL - priced out <$250, provided 7,000 miles (via EWR or IAD)
SFO/ORD - priced out <$120, provided 3,700 miles