I have a full day in Nairobi before my trip to the CAR begins. Is there anyone with first hand experience with a Kenyan tour company which does (private) day tours? I am looking to go to Lake Nakuru or Lake Elementaita (Kenya Lake System WHS) for the day.

Oh -- I'm sorry this didn't work out, Els.

I was researching the Tentative Lists to get ideas for African nominations for Top 50 - 2020, and noticed a couple tentative sites still listed on the Kenya page that I think can be removed since they have been inscribed. The Kenya Lake System in the Great Rift Valley was inscribed in 2011, which I think fulfills The Great Rift Valley - The Kenya Lakes System site on the T-list (I'm not sure why it still is listed on the UNESCO page as a tentative site).

Additionally, the Lake Nakuru National Park and Lake Bogoria National Reserve sites on the T-list appear to be captured in The Kenya Lake System in the Great Rift Valley WHS, according to the map from the UNESCO site and the maps of the boundaries of Lake Nakuru National Park and Lake Bogoria National Reserve.

Hope you get to visit this site soon -- it looks amazing!

Yes, that's why I keep them up as well - to keep it 1-on-1 with the UNESCO list (though it is in error in Kenya's T List)
There's a connection about it also, Already inscribed, still on T List

Interesting -- I guess Kenya needs to clean up their T-list. Thanks!

Plans underway to list Gede ruins as world heritage site

No specific year is given for the proposal, but it seems the Gede/Gedi ruins are already some steps into the process.

https://www.kenyanews.go.ke/push-for-taita-skulls-caves-to-world-heritage-sites-begin/
Ancient skull caves of Taita-Taveta County may be brought forward by Kenya in the coming years.

Normally I don't post my trips but I'm a bit shocked how underused the Kenyan parks and sites are. Most travelers seems foreign residents who just make the best of what they get domestically thus Malindi getting attention even though the beach is not super exciting, or Shela being a party spot at the east coast.

* all parks are paid through eCitizen (like your visa) and if you didn't/can't usually you can pay someone to transfer Mpesa mobile cash to pay it ) they'll want 100 shillings commission)
* Safaricom has the best coverage around the country
* Charter flight doesn't mean my private plane but it's not booked online and you need to ask tour agencies what is running. There are some at the airport on arrival for this already. The biplanes saved me a day and I would have skipped Lake Turkana and fly from Maasai Mara to Wilson instead, then Wilson to the lake.
* many parks don't need 4WD but I recommend it. Local Kenya tourists drive through with their beat up city cruiser - crazy
* The mainstream rental companies won't allow national park entry so book with a specialized one
* Airports will always have someone with transportation available, just negotiate and maybe throw in gas money

D1 Nairobi -> Migori
grab driver to Thimlich Ohinga Historic Site WHS
driver back to Migori (long daytrip)
ON Migori
D2+3 2D Tour into Maasai Mara NR
D4 charter flight to Loiyangalani early morning
grab driver to Lake Turkana
grab dinghy for Tukana South Island WHS tour
driver back to airport
charter flight to Nairobi Wilson late afternoon
rent 4WD
ON Lake Naivasha
D5 Hell's Gate NP Cycle, Ganedrive + Hotsprings (opens 6am)
ON Nakuru
D6 Lake Nakuru WHS (Kenya Lake System) Morning Gamedrive (opens 6:30, max 4h)
2h Drive to Aberdare Range NP Mutubio West Gate
3h drive through Aberdare Range exit Treetops Gate
ON near Naro Moru
D7 Mount Kenya NP WHS
4h drive to Nairobi
ON East Nairobi
D8 Amboseli NP
Return Car Nairobi Airport
ON Nairobi Airport (don't stay in town, it's a long way)
D9 Flight to Lamu
Lamu WHS Tour (2h)
ON Lamu Old Town
D10 Flight to Mombasa early morning
Rent 2WD Car ($20 per day!)
Fort Jesus WHS (max 1~2h)
Gedi Ruins
ON Mida Creek
D11 Arabuko Sokoke NR (Coastal Forests tWHS) full day tour (3h hike + game drive)
ON Mida Creek
D12 Morning Canoe trip Mida Creek
Panga Saidi Cave
Kaya Kaumi WHS (Mijikenda Kaya Forests)
Mawe Meru Black Rocks/Cave
Return Car Mombasa Airport
Flight back to Nairobi 8pm + onwards next morning

Could have added Mount Kulal Biosphere Reserve but road is long and visit means hiking so that's an rxtra 2 days and for tentative that looks just so-so I wasn't prepared to invest time on this trip, was already happy the flights worked out well
Was thinking of driving all the way east but it would need a trek back and one has to fly to Lamu anyway as shouldn't drive to the region across the water due to safety

Here's my public transport based itinerary along 7 of Kenya's WHS, which I just finished. More tips to follow in Sunday's blog post.

Itinerary
D1 – Arrival Mombasa Airport in the early morning. Official taxi to hotel (1,400 KSh). Later tuktuk (150 KSh) to Fort Jesus WHS. Went on from there on foot through Old Mombasa with some fine buildings such as the Post Office. ON Mombasa.
D2 – Tour with Diani Summer Tours (driver-only) to Kaya Kauma (WHS), 7.00-13.00 (150 EUR). ON Mombasa.
D3 – Matatu from Buxton bus station (Malindi-bound) to Gedi (600 KSh/2h). Moto to Gedi ruins (100 KSh). After visiting the WHS (500 KSh/1h), moto to Watamu (400 KSh). ON Watamu.
D4 – Planned for Araboku Sokoro Forest TWHS, but it rained for most of the day. ON Watamu.
D5 – Private transfer to Mombasa Airport (8,000 KSh/2h) to catch the 11.15 am flight to Lamu with Skyward Express. ON Lamu.
D6 – Guided walk around town arranged by my guesthouse (3,000 Ksh/2h). More exploration on my own and Lamu Museum (550 Ksh) later in the day. ON Lamu.
D7 – Flight to Nairobi with Jambojet. Shared taxi (could not find the airport bus) to CBD (100 Ksh). ON Nairobi.
D8 – Matatu from Nairobi's Tea Room station to Naro Moru (680 KSh/3h). ON Naro Moru.
D9 – Chilling around the lodge, with a bit of birding and walking the nature trail. ON Naro Moru.
D10 – Day tour to Ngare Ndare Forest (Mount Kenya WHS) via lodge, 250 USD all-inclusive. ON Naro Moru.
D11 – Matatu to Nakuru, via Nyeri (2h45/700 KSh; there are also direct ones from Naro Moru but less frequent). ON Nakuru
D12 – Half-day tour (6-13) to Lake Nakuru National Park with Pega Tours (120 USD + 60 USD entrance fee). ON Nakuru
D13 – Easy Coach bus to Kisumu (1400 KSh/3.5h). ON Kisumu
D14 – Full day tour to Thimlich Ohinga, organized by Great Horizon Trails (235 USD all-inclusive). ON Kisumu
D15 – Early morning flight from Kisumu to Nairobi. Flight back home from there.

I booked the private day tours about a week beforehand, choosing local companies with an office in the hub town.
Another thing to note is which month to go. July to October are the most popular months, as it is the dry season and when the wildebeest migration takes place. June is a good transitional month to go, I only lost 1 day due to rain. Parks and accommodations sometimes differ between high and low season rates, so in that way you're good with June as well.

Did you book the tours in person or online?

Online, via e-mail. I usually sent the money beforehand via Wise (or M-Pesa via Wise).