Places where the revolutionary government and/or project are more or less intact. That way you can help support the people who live there at the same time you make connections or learn about other cultures. You can also use this opportunity to learn about which groups are legit or not so that you can set up recurring donations to their projects. Sometimes there's really no way to do that outside of visiting in-person or already having local comrades.

You could also support groups dedicated to opposing neoliberalization and displacement are safe bets. Places dedicated to making indigenous ways of life economically viable and therefore sustainable, for example. Often, indigenous communities lose their children to cities and tourism because the money is better, leading to a kind of slow genocide via the economy itself.

Countries that come to mind, in no particular order:

• Cuba
• Vietnam
• Laos
• Venezuela (in particular, the communes)
• Bolivia (visiting indigenous workers, socialists, and probably also just La Paz)
• You can visit communist neighborhoods and projects in most Latin American countries
• China. It's doing relatively well economically but there are still a ton of extremely poor people there and active projects to improve their lives. You can find a town and its party representative(s) and contact them in advance to do a visit and ask how you could contribute.