Scandinavia trip planning questions

1 Google maps is a good start, or do you prefer a paper map.

2 I've not too familiar with guide books on Scandinavia but I can't recommend Rick Steves' book. He focuses a lot on a couple of places and don't even mention other.

4 Yes, several. What kind of areas do you prefer? Coastal? Mountains? Forests? And how long hikes? Short day trips or week long trips? Easy walks suitable for everyone or more rugged terrain? Close to civilization or far away from towns and cities?

Also note that Iceland and Finland are not part of Scandinavia.

"Nordic" would be inclusive of Finland and Iceland. That said, what are you looking for in a "good travel map"? What is your prefered travel mode? What will you be using the travel map for?

Prior to my first trip to Norway I used a paper AAA Scandinavia and Baltic States map for orientation and location purposes. Google Maps has since replaced paper maps for my planning in that Google will locate small towns and villages. Google Maps is also a good start for identifying alternative modes of travel.
https://www.amazon.com/Scandinavia-Baltic-States-Including-Lithuania/dp/1562518518

If you want detailed Norway trekking/ski touring topographic maps: https://english.dnt.no/maps/

For Denmark, are there any national parks or nature areas with hiking
that are easily accessible by public transportation?

If you are in Copenhagen you can easily visit "Dyrehaven" for a day trip. Take an S-train to Klampenborg, leave the station and turn left. if it is summer you can also visit Bakken.

For a longer trip (several days) I recommend you arrange something with http://vt-dk.dk/en or some other company. Almost everywhere in Denmark is easily accessible by public transportation

I have visited all the countries that you mentioned except Finland.
We did Estonia in 2011 after a Russian River Cruise. We also visited Latvia and Lithuania. Estonia is a small country but even in 2011 the economic progress it made after being a part of the decrepit Soviet Union was remarkable. Tallinn is full of history and worth a couple of days. Can't comment on hiking opportunities.

We did Iceland in 2014 while on a cruise. We were there for one day and did an excellent tour called the Golden Circle. I highly recommend that tour. An internet search will display more than one tour company.

We have been to Denmark three times and enjoyed that country quite a bit. Copenhagen is worth 3 days minimum and we enjoyed a tour that visited the countryside as well as the Viking Museum and a couple of historic castles among other things. Take a canal tour of Copenhagen while there and visited the Royal Palace and saw the changing of the guard.

We spent two days in Stockholm prior to our 11 night cruise of Norway. Loved the Vasa Museum. Be sure and stay near the old city where the Royal Palace is located.

We had visited Bergen, Norway on a cruise in 2014 for a day, it was nice and we had a great walking tour. In 2019, we did a 11 night cruise from Copenhagen of Norway, all the way to the North Cape. We visited 6 ports and it was wonderful. That was a great way to see Norway. Norway is fairly mountainous and even in June, we were told that there was a snowstorm that closed highways on mountain roads in the south. There is rail service between some of the cities in the south that is good. I suspect the hiking season is fairly short there.

Reply to Badger:

Yes, several. What kind of areas do you prefer? Coastal? Mountains?
Forests? And how long hikes? Short day trips or week long trips? Easy
walks suitable for everyone or more rugged terrain? Close to
civilization or far away from towns and cities?

I would like to do some day hikes. The landscape doesn't matter. I won't have a car so I'll be limited to public transportation (e.g. train, bus).

Day hikes accessible by transit:

Oslo, Norway. The Oslo Nordmarka (north forest) is accessible by the Metro.
https://www.visitoslo.com/en/articles/nordmarka-forest/

Nordmarka forest The vast areas of untouched nature that surround
Oslo are just 20-30 minutes from the city centre.

Some good starting points for outdoor experiences in the wilderness
include Holmenkollen, Frognerseteren, Sørkedalen, and Sognsvann. You
can easily reach these places with public transportation, and once you
get there, you have many possible activities in front of you!

https://www.atlasandboots.com/oslo-hiking-trails-metro-t-bane/

A comprehensive network of Oslo hiking trails is accessible from the
city metro system. All offer great access to the outdoors and are easy
to reach from the city centre

The hiking trails around Oslo are similar to those in the rest of the
country: clearly signposted, well maintained and often bookended with
cosy cabins serving hot drinks and hearty food.

For information visit Oslo's The Norwegian Trekking Association (DNT Oslo og Omegn) office a couple of blocks from the Oslo S train station for maps and advice:
Storgata 3, 0155 Oslo, Norway
https://www.visitoslo.com/en/product/?TLp=659878

Helsinki, Finland
Suomenlinna Island is a ferry ride from Helsinki.
https://www.suomenlinna.fi/en/

https://www.suomenlinna.fi/en/visitor/faq/

The Helsinki City Transport ferry operates throughout the year to
Suomenlinna. The ferry journey takes about 15 minutes. During the
summer season, you can also get to Suomenlinna on the waterbus
operated by JT-Line, which stops at the Artillery Bay pier and the
King’s Gate.

Easy hiking.walking around the island. Download hiking maps/routes.
https://hikepack.earth/maps/FI-34/Suomenlinna

Suomenlinna (Finnish), or Sveaborg (Swedish), literal translation
Finland Castle, until 1918 Viapori (Finnish), is an inhabited sea
fortress built on six islands and which now forms part of the city of
Helsinki. Suomenlinna is a UNESCO World Heritage site and popular with
tourists and locals, who enjoy it as a picturesque picnic site.
Suomenlinna is now one of the most popular tourist attractions in
Helsinki as well as a popular picnicking spot for the city's
inhabitants

For day hikes in Sweden that do not require a car there are still quite a lot to choose from. But a few suggestions:

• Siljansleden, a hiking trail around lake Siljan. In total 340 km but you can walk as long or short as you like. It passes several towns that are well connected to each other by train.
• Kungsleden, a 400 km trail through the Lapland mountains but possible to do shorter parts of it as well.
• Höga kusten-leden. The High Coast trail, south of Örnsköldsvik. A very scenic area.
• Skåneleden, especially the Österlen part.
• Upplandsleden, especially the Fjällnora-Länna-Almunge part than can easily be combined with a trip with the Lennakatten steam train.
• If you are interested in the history of science, there are also the Linnétrails around Uppsala that Linneaus used to walk with his students to teach them botany.