Kaliningrad was the only place I've been, as this is the center of the Kaliningrad region.
Since the summer of 2019 there is a simplified visa that can be used to enter the Kaliningrad region. It's fully electronic, free, but short-term and can be used for this region only. But it's surprisingly easy to apply, just go to the website, fill in the form and in a few days you'll get the visa in PDF.
You'll need a photo of yourself and a bunch of basic details. One question was where I intended to stay and I wasn't sure that meant I need to book in advance or it's just an intention. I decided not to book the accomodation and get the visa first, and I got it without any issues.
I got the visa before the deadline and it was a quite pleasant process. I got an email informing me about the status, then I printed it and had absolutely no problems at the border. Even though it should work on a phone, I recommend printing it. And make sure you keep it until you've left as they asked for the visa upon exiting the country.
Overall it's a surprisingly unbureaucratic process. But make sure you scrutinize the fine print as there are some important details. Not all countries are on the whitelist, most notably the US and the UK are missing. Also, it's for a single entry and the validity is also rounded to the start of the day.
I took a bus from Nida, Lithuania when I came to Kaliningrad. There is a timetable at the bus station and I could buy the ticket in advance. The bus was on-time, and it took ~3 hours to drop me at the Kaliningrad station.
When I left Russia I went to Gdansk by bus. There are serveral companies serving this route. The one I chose had its timetables online but for some unknown reason I could not buy a ticket electronically. But I went to the bus station and there is an international booth where I could buy the ticket in advance.
The bus station is secured with an x-ray machine similar to what you can find in airports. You need to put your backpack and other metal stuff onto the conveyor belt then walk through the metal detector then pick your belongings on the other end. There was one guard supervising the process, and it's quite fast.
In the city, buses go everywhere. As for tickets, you pay at the conductor when they come. There are timetables and maps, so it's quite easy and cheap to get around. Just don't expect much comfort as the vehicles are old and unmaintained.
Walking around is way less pleasant than in other places. I had the impression that everything is built around cars here with little thoughts on pedestrians. Crossings are rare and therer are places where they are missing completely.
The Kant Island is a nice exception, but Kaliningrad has no definitive center with all the sights packed together in walking distance.
While the neighbouring countries observe daylight saving time at least for now, Russia does not. This makes a strange situation where during the summer it aligns with Poland, and during the winter with Lithuania.
A nice historical touch is that Euler laid the foundation of graph theory by walking the bridges of Kaliningrad, then Konigsberg. He coined the Eulerian path which is something I learned about in University math.
I stayed in a hostel a bit farther away from the center and it was filled with locals. Even families with children lived there which was quite strange at first.
This wasn't bad actually, all of the people there were really nice, though they didn't speak much English. And while lacking the social atmosphere, it had a laid-back feeling and was sufficiently calm for sleeping.
A museum among the houses with some weapons outside. If you don't know there is something of interest behind the building you wouldn't find it.
I didn't go in, I believe it was closed but it might worth a visit.
The Homlins are small sculptures in different parts of the city. They are sctually advertisements for a local shop that makes souvenirs. But these small statues add a nice touch to exploring the city and they feel like collectibles.
At the time of writing there were 3 statues, but only 2 of them were in place when I was visiting Kaliningrad. I believe more are yet to come.
Just like in Tirana, it seems like no post-communist city is complete without a grandiose building totally abandoned and left to decay. In Tirana, it was the Pyramid of Tirana, here it is the House of Soviets.
Originally built to house the local party elite in a luxurious way, but it wasn't finished at all and thus was never used.
Today, it occupies in prime real estate, close to the city center as a reminder of useless and wasteful giant constructions. I've heard there are plans to demolish it, but there is no consensus what to do with it.
This is the green sport in the center of the city, nestled between the two rivers. The whole island is a park with the Cathedral the only building here.
It's strange to see the old photograpsh put into display along the main pedestrian road, showing all the houses that were standing there. During WW2 the island was bombed and later rebuilt into a park.
This is the perfect place for a walk in the green and to visit Kant's Tomb.
In the center you'll definitely see the ships and the building of the Ocean Museum. They are quite a sight even without going inside.
There are some weapons, small submarines, and other things displayed in the garden.
A peculiar building in a park not far from the center. It's built upside down, it even has a car parking next to it hanging from the top.
The defacto city center, it's a giangt square with a monument and a church. It is called "Victory square" because it was built when the USSR won WW2.