According to a South Korean newspaper, cited by Reuters

The report says that US State Department officials have recently met multiple times with North Korean counterparts in Hanoi, Vietnam discussing plans for a second summit between Trump and Kim Jong Un.

It further says that they discussed the schedule for said summit to take place with the possibility that Vietnam could host the event since it has diplomatic relations with both US and North Korea. Over the weekend, Trump did make a mention saying that they are negotiating a location for a second summit so this is just a follow up to that it seems.

Guess we're going to have another play date real soon. I reckon it will pretty much end in a similar fashion as the first one did though.